Functions & Scope

Default Arguments

Optional Parameters

Your greet() function usually says "Hello" but sometimes needs "Hi" or "Hey". Default arguments let callers omit parameters when the default is fine, while still allowing customization when needed.

Basic default values

Give parameters default values.

greet.py
Replay: real traced execution (multi-file project)
def main():
    print("=== Default Arguments ===\n")

    # Without default - must provide both
    greet_formal("Alice", "Good morning")

    # With default - greeting is optional
    greet("Bob")                    # Uses default "Hello"
    greet("Charlie", "Hey")         # Overrides default
    greet("Diana", "Good evening")

    print("\n=== Common Pattern ===")
    # Default makes common case simple
    # Special cases still possible

    greet("Everyone")  # 90% of calls use default
    greet("VIP", "Welcome, dear")  # 10% need custom

def greet_formal(name, greeting):
    """Both arguments required."""
    print(f"{greeting}, {name}!")

def greet(name, greeting="Hello"):
    """greeting has default value."""
    print(f"{greeting}, {name}!")

def greet_polite(name, greeting="Hello", punctuation="!"):
    """Multiple defaults."""
    print(f"{greeting}, {name}{punctuation}")

if __name__ == "__main__":
    main()

  1. def main():

    1#@var=default,formal2def main():3    print("=== Default Arguments ===\n")4    5    # Without default - must provide both  #?greet6    greet_formal("Alice", "Good morning")
    output=== Default Arguments ===

  2. def greet_formal(name, greeting): #?required

    5    # Without default - must provide both  #?greet6    greet_formal("Alice", "Good morning")7    8    # With default - greeting is optional9    greet("Bob")                    # Uses default "Hello"10    greet("Charlie", "Hey")         # Overrides default11    greet("Diana", "Good evening")12    13    print("\n=== Common Pattern ===")14    # Default makes common case simple15    # Special cases still possible16    17    greet("Everyone")  # 90% of calls use default18    greet("VIP", "Welcome, dear")  # 10% need custom1920def greet_formal(nameAlice, greetingGood morning):  #?required21    """Both arguments required."""22    print(f"{greetingGood morning}, {nameAlice}!")
    outputGood morning, Alice!

  3. def greet(name, greeting="Hello"): #?default

    pass 1 of 5
    8    # With default - greeting is optional9    greet("Bob")                    # Uses default "Hello"10    greet("Charlie", "Hey")         # Overrides default11    greet("Diana", "Good evening")12    13    print("\n=== Common Pattern ===")14    # Default makes common case simple15    # Special cases still possible16    17    greet("Everyone")  # 90% of calls use default18    greet("VIP", "Welcome, dear")  # 10% need custom1920def greet_formal(name, greeting):  #?required21    """Both arguments required."""22    print(f"{greeting}, {name}!")2324def greet(nameBob, greetingHello="Hello"):  #?default25    """greeting has default value."""26    print(f"{greetingHello}, {nameBob}!")
    outputHello, Bob!
    All 5 passes — pass 1 is the card above
    passnamegreeting
    1BobHello
    2CharlieHey
    3DianaGood evening
    4EveryoneHello
    5VIPWelcome, dear

  4. main()

    34if __name__ == "__main__":35    main()36#@help greet

Parameters with defaults can be omitted when calling the function.

default argument Parameter with preset value: `def f(x=10):`. Used if caller doesn't provide.

Keyword arguments skip positional defaults

Use keyword syntax to specify later parameters.

keyword_args.py
Replay: real traced execution (multi-file project)
def main():
    print("=== Keyword Arguments ===\n")

    # Positional: order matters
    print("Positional order:")
    describe_pet("Hamster", "Harry")
    describe_pet("Dog", "Buddy")

    # Keyword: name=value, order doesn't matter
    print("\nKeyword arguments:")
    describe_pet(pet_name="Whiskers", animal_type="Cat")
    describe_pet(animal_type="Fish", pet_name="Nemo")     # Reversed!

    # Mix positional and keyword
    print("\nMixed:")
    describe_pet("Rabbit", pet_name="Thumper")

    # Skip middle defaults with keywords!
    print("\nSkipping defaults:")
    format_text("hello world", uppercase=True)  # Skip width
    format_text("hello world", width=20)        # Skip uppercase
    format_text("hello world", uppercase=True, width=15)  # All specified

def describe_pet(animal_type, pet_name):
    """Describe a pet."""
    print(f"  I have a {animal_type} named {pet_name}.")

def format_text(text, width=0, uppercase=False):
    """Format text with optional width and case."""
    result = text.upper() if uppercase else text
    if width > 0:
        result = result.center(width)
    print(f"  '{result}'")

if __name__ == "__main__":
    main()

  1. def main():

    1#@var=default,explicit2def main():3    print("=== Keyword Arguments ===\n")4    5    # Positional: order matters6    print("Positional order:")7    describe_pet("Hamster", "Harry")    #?positional8    describe_pet("Dog", "Buddy")
    output=== Keyword Arguments ===
Positional order:

  2. def describe_pet(animal_type, pet_name):

    pass 1 of 5
    6    print("Positional order:")7    describe_pet("Hamster", "Harry")    #?positional8    describe_pet("Dog", "Buddy")9    10    # Keyword: name=value, order doesn't matter11    print("\nKeyword arguments:")12    describe_pet(pet_name="Whiskers", animal_type="Cat")  #?keyword13    describe_pet(animal_type="Fish", pet_name="Nemo")     # Reversed!14    15    # Mix positional and keyword  #?mix16    print("\nMixed:")17    describe_pet("Rabbit", pet_name="Thumper")18    19    # Skip middle defaults with keywords!  #?skip20    print("\nSkipping defaults:")21    format_text("hello world", uppercase=True)  # Skip width22    format_text("hello world", width=20)        # Skip uppercase23    format_text("hello world", uppercase=True, width=15)  # All specified  #@var=_,!2425def describe_pet(animal_typeHamster, pet_nameHarry):26    """Describe a pet."""27    print(f"  I have a {animal_typeHamster} named {pet_nameHarry}.")
    output  I have a Hamster named Harry.
    All 5 passes — pass 1 is the card above
    passanimal_typepet_namewidthresult
    1HamsterHarry——
    2DogBuddy——
    3CatWhiskers——
    4FishNemo——
    5RabbitThumper20hello world → hello world

  3. result ← HELLO WORLD

    pass 1 of 3
    20    print("\nSkipping defaults:")21    format_text("hello world", uppercase=True)  # Skip width22    format_text("hello world", width=20)        # Skip uppercase23    format_text("hello world", uppercase=True, width=15)  # All specified  #@var=_,!2425def describe_pet(animal_type, pet_name):26    """Describe a pet."""27    print(f"  I have a {animal_type} named {pet_name}.")2829def format_text(texthello world, width0=0, uppercaseTrue=FalseFalse):  #?format30    """Format text with optional width and case."""31    result→ HELLO WORLD = texthello world.upper() if uppercaseTrue else text32    if width > 0:33        result = result.center(width)34    print(f"  '{resultHELLO WORLD}'")
    output  'HELLO WORLD'
    All 3 passes — pass 1 is the card above
    passwidthuppercaseresult
    10TrueHELLO WORLD
    220Falsehello world
    315TrueHELLO WORLD

  4. result ← hello world

    pass 1 of 2
    31result = text.upper() if uppercase else text32if width20 > 0:33    result→     hello world      = result.center(width20)34print(f"  '{result}'")

  5. print(f" '{result}'")

    21    format_text("hello world", uppercase=True)  # Skip width22    format_text("hello world", width=20)        # Skip uppercase23    format_text("hello world", uppercase=True, width=15)  # All specified  #@var=_,!2425def describe_pet(animal_type, pet_name):26    """Describe a pet."""27    print(f"  I have a {animal_type} named {pet_name}.")2829def format_text(text, width=0, uppercase=False):  #?format30    """Format text with optional width and case."""31    result = text.upper() if uppercase else text32    if width > 0:33        result = result.center(width)34    print(f"  '{result    hello world     }'")
    output  '    hello world     '

  6. result ← HELLO WORLD

    pass 2 of 2
    31result = text.upper() if uppercase else text32if width15 > 0:33    result→   HELLO WORLD   = result.center(width15)34print(f"  '{result}'")

  7. print(f" '{result}'")

    22    format_text("hello world", width=20)        # Skip uppercase23    format_text("hello world", uppercase=True, width=15)  # All specified  #@var=_,!2425def describe_pet(animal_type, pet_name):26    """Describe a pet."""27    print(f"  I have a {animal_type} named {pet_name}.")2829def format_text(text, width=0, uppercase=False):  #?format30    """Format text with optional width and case."""31    result = text.upper() if uppercase else text32    if width > 0:33        result = result.center(width)34    print(f"  '{result  HELLO WORLD  }'")
    output  '  HELLO WORLD  '

  8. main()

    36if __name__ == "__main__":37    main()38#@help positional

func(c=30) skips a and b if they have defaults.

Multiple default parameters

Functions can have several parameters with defaults.

example
multiple_defaults.py
Replay: real traced execution (multi-file project)
def main():
    print("=== Multiple Default Arguments ===\n")

    # Using all defaults
    print("All defaults:")
    make_coffee()

    # Override some
    print("\nCustom orders:")
    make_coffee(size="large")
    make_coffee(milk=True)
    make_coffee(sugar=2)
    make_coffee(size="small", sugar=3)

    # Override all
    print("\nFully customized:")
    custom_size = "large"
    sugar_count = 2
    make_coffee(custom_size, True, sugar_count)  # positional
    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword

    # Configuration pattern
    print("\n=== Configuration Pattern ===")
    print_report()
    print_report(title="Sales Report", columns=3)
    print_report(show_header=True, title="Status")

def make_coffee(size="medium", milk=False, sugar=0):
    """Make coffee with customizable options."""
    order = f"  {size.capitalize()} coffee"
    if milk:
        order += " with milk"
    if sugar > 0:
        order += f", {sugar} sugar(s)"
    print(order)

def print_report(title="Report", columns=2, show_header=False):
    """Print a configurable report."""
    if show_header:
        print(f"  === {title} ===")
    else:
        print(f"  {title}")
    print(f"  ({columns} columns)")

if __name__ == "__main__":
    main()

def main():
    print("=== Multiple Default Arguments ===\n")

    # Using all defaults
    print("All defaults:")
    make_coffee()

    # Override some
    print("\nCustom orders:")
    make_coffee(size="large")
    make_coffee(milk=True)
    make_coffee(sugar=2)
    make_coffee(size="small", sugar=3)

    # Override all
    print("\nFully customized:")
    custom_size = "small"
    sugar_count = 2
    make_coffee(custom_size, True, sugar_count)  # positional
    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword

    # Configuration pattern
    print("\n=== Configuration Pattern ===")
    print_report()
    print_report(title="Sales Report", columns=3)
    print_report(show_header=True, title="Status")

def make_coffee(size="medium", milk=False, sugar=0):
    """Make coffee with customizable options."""
    order = f"  {size.capitalize()} coffee"
    if milk:
        order += " with milk"
    if sugar > 0:
        order += f", {sugar} sugar(s)"
    print(order)

def print_report(title="Report", columns=2, show_header=False):
    """Print a configurable report."""
    if show_header:
        print(f"  === {title} ===")
    else:
        print(f"  {title}")
    print(f"  ({columns} columns)")

if __name__ == "__main__":
    main()

def main():
    print("=== Multiple Default Arguments ===\n")

    # Using all defaults
    print("All defaults:")
    make_coffee()

    # Override some
    print("\nCustom orders:")
    make_coffee(size="large")
    make_coffee(milk=True)
    make_coffee(sugar=2)
    make_coffee(size="small", sugar=3)

    # Override all
    print("\nFully customized:")
    custom_size = "large"
    sugar_count = 1
    make_coffee(custom_size, True, sugar_count)  # positional
    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword

    # Configuration pattern
    print("\n=== Configuration Pattern ===")
    print_report()
    print_report(title="Sales Report", columns=3)
    print_report(show_header=True, title="Status")

def make_coffee(size="medium", milk=False, sugar=0):
    """Make coffee with customizable options."""
    order = f"  {size.capitalize()} coffee"
    if milk:
        order += " with milk"
    if sugar > 0:
        order += f", {sugar} sugar(s)"
    print(order)

def print_report(title="Report", columns=2, show_header=False):
    """Print a configurable report."""
    if show_header:
        print(f"  === {title} ===")
    else:
        print(f"  {title}")
    print(f"  ({columns} columns)")

if __name__ == "__main__":
    main()

def main():
    print("=== Multiple Default Arguments ===\n")

    # Using all defaults
    print("All defaults:")
    make_coffee()

    # Override some
    print("\nCustom orders:")
    make_coffee(size="large")
    make_coffee(milk=True)
    make_coffee(sugar=2)
    make_coffee(size="small", sugar=3)

    # Override all
    print("\nFully customized:")
    custom_size = "large"
    sugar_count = 3
    make_coffee(custom_size, True, sugar_count)  # positional
    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword

    # Configuration pattern
    print("\n=== Configuration Pattern ===")
    print_report()
    print_report(title="Sales Report", columns=3)
    print_report(show_header=True, title="Status")

def make_coffee(size="medium", milk=False, sugar=0):
    """Make coffee with customizable options."""
    order = f"  {size.capitalize()} coffee"
    if milk:
        order += " with milk"
    if sugar > 0:
        order += f", {sugar} sugar(s)"
    print(order)

def print_report(title="Report", columns=2, show_header=False):
    """Print a configurable report."""
    if show_header:
        print(f"  === {title} ===")
    else:
        print(f"  {title}")
    print(f"  ({columns} columns)")

if __name__ == "__main__":
    main()

  1. def main():

    1#@var=default,config2def main():3    print("=== Multiple Default Arguments ===\n")4    5    # Using all defaults  #?alldefault6    print("All defaults:")7    make_coffee()
    output=== Multiple Default Arguments ===
All defaults:

  2. order ← Medium coffee

    pass 1 of 7
    6    print("All defaults:")7    make_coffee()8    9    # Override some  #?override10    print("\nCustom orders:")11    make_coffee(size="large")12    make_coffee(milk=True)13    make_coffee(sugar=2)14    make_coffee(size="small", sugar=3)15    16    # Override all17    print("\nFully customized:")18    custom_size = "large"  #@custom_size="small"19    sugar_count = 2  #@sugar_count=1, 320    make_coffee(custom_size, True, sugar_count)  # positional21    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword22    23    # Configuration pattern  #@var=_,!24    print("\n=== Configuration Pattern ===")  #@var=_,!25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(sizemedium="medium", milkFalse=FalseFalse, sugar0=0):  #?params30    """Make coffee with customizable options."""31    order→   Medium coffee = f"  {sizemedium.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order  Medium coffee)
    output  Medium coffee

Custom orders:
    All 7 passes — pass 1 is the card above
    passsizemilksugarorder
    1mediumFalse0 Medium coffee
    2largeFalse0 Large coffee
    3mediumTrue0 Medium coffee
    4mediumFalse2 Medium coffee
    5smallFalse3 Small coffee
    6largeTrue2 Large coffee
    7largeTrue2 Large coffee

  3. order ← Medium coffee with milk

    pass 1 of 3
    31order = f"  {size.capitalize()} coffee"32if milkTrue:33    order→   Medium coffee with milk += " with milk"34if sugar > 0:
    All 3 passes — pass 1 is the card above
    passorder
    1 Medium coffee → Medium coffee with milk
    2 Large coffee → Large coffee with milk
    3 Large coffee → Large coffee with milk

  4. print(order)

    11    make_coffee(size="large")12    make_coffee(milk=True)13    make_coffee(sugar=2)14    make_coffee(size="small", sugar=3)15    16    # Override all17    print("\nFully customized:")18    custom_size = "large"  #@custom_size="small"19    sugar_count = 2  #@sugar_count=1, 320    make_coffee(custom_size, True, sugar_count)  # positional21    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword22    23    # Configuration pattern  #@var=_,!24    print("\n=== Configuration Pattern ===")  #@var=_,!25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order  Medium coffee with milk)
    output  Medium coffee with milk

  5. order ← Medium coffee, 2 sugar(s)

    pass 1 of 4
    33    order += " with milk"34if sugar2 > 0:35    order→   Medium coffee, 2 sugar(s) += f", {sugar2} sugar(s)"36print(order)
    All 4 passes — pass 1 is the card above
    passsugarorder
    12 Medium coffee → Medium coffee, 2 sugar(s)
    23 Small coffee → Small coffee, 3 sugar(s)
    32 Large coffee with milk → Large coffee with milk, 2 sugar(s)
    42 Large coffee with milk → Large coffee with milk, 2 sugar(s)

  6. print(order)

    12    make_coffee(milk=True)13    make_coffee(sugar=2)14    make_coffee(size="small", sugar=3)15    16    # Override all17    print("\nFully customized:")18    custom_size = "large"  #@custom_size="small"19    sugar_count = 2  #@sugar_count=1, 320    make_coffee(custom_size, True, sugar_count)  # positional21    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword22    23    # Configuration pattern  #@var=_,!24    print("\n=== Configuration Pattern ===")  #@var=_,!25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order  Medium coffee, 2 sugar(s))
    output  Medium coffee, 2 sugar(s)

  7. custom_size ← large, sugar_count ← 2

    13    make_coffee(sugar=2)14    make_coffee(size="small", sugar=3)15    16    # Override all17    print("\nFully customized:")18    custom_size→ large = "large"  #@custom_size="small"19    sugar_count→ 2 = 2  #@sugar_count=1, 320    make_coffee(custom_sizelarge, True, sugar_count2)  # positional21    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword22    23    # Configuration pattern  #@var=_,!24    print("\n=== Configuration Pattern ===")  #@var=_,!25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order  Small coffee, 3 sugar(s))
    output  Small coffee, 3 sugar(s)

Fully customized:

  8. print(order)

    19    sugar_count = 2  #@sugar_count=1, 320    make_coffee(custom_sizelarge, True, sugar_count2)  # positional21    make_coffee(size=custom_sizelarge, milk=True, sugar=sugar_count2)  # keyword22    23    # Configuration pattern  #@var=_,!24    print("\n=== Configuration Pattern ===")  #@var=_,!25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order  Large coffee with milk, 2 sugar(s))
    output  Large coffee with milk, 2 sugar(s)

  9. print(order)

    20    make_coffee(custom_size, True, sugar_count)  # positional21    make_coffee(size=custom_sizelarge, milk=True, sugar=sugar_count2)  # keyword22    23    # Configuration pattern  #@var=_,!24    print("\n=== Configuration Pattern ===")  #@var=_,!25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order  Large coffee with milk, 2 sugar(s))
    output  Large coffee with milk, 2 sugar(s)

=== Configuration Pattern ===

  10. def print_report(title="Report", columns=2, show_header=False):

    pass 1 of 3
    38#@var=_,!39def print_report(titleReport="Report", columns2=2, show_headerFalse=FalseFalse):40    """Print a configurable report."""41    if show_header:
    All 3 passes — pass 1 is the card above
    passtitlecolumnsshow_header
    1Report2False
    2Sales Report3False
    3Status2True

  11. else:

    pass 1 of 2
    41if show_header:42    print(f"  === {title} ===")43else:44    print(f"  {titleReport}")45print(f"  ({columns} columns)")
    output  Report

  12. print(f" ({columns} columns)")

    24    print("\n=== Configuration Pattern ===")  #@var=_,!25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order)3738#@var=_,!39def print_report(title="Report", columns=2, show_header=False):40    """Print a configurable report."""41    if show_header:42        print(f"  === {title} ===")43    else:44        print(f"  {title}")45    print(f"  ({columns2} columns)")46#@var=_,!
    output  (2 columns)

  13. else:

    pass 2 of 2
    41if show_header:42    print(f"  === {title} ===")43else:44    print(f"  {titleSales Report}")45print(f"  ({columns} columns)")
    output  Sales Report

  14. print(f" ({columns} columns)")

    25    print_report()  #@var=_,!26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order)3738#@var=_,!39def print_report(title="Report", columns=2, show_header=False):40    """Print a configurable report."""41    if show_header:42        print(f"  === {title} ===")43    else:44        print(f"  {title}")45    print(f"  ({columns3} columns)")46#@var=_,!
    output  (3 columns)

  15. if show_header:

    40"""Print a configurable report."""41if show_headerTrue:42    print(f"  === {titleStatus} ===")43else:
    output  === Status ===

  16. print(f" ({columns} columns)")

    26    print_report(title="Sales Report", columns=3)  #@var=_,!27    print_report(show_header=True, title="Status")  #@var=_,!2829def make_coffee(size="medium", milk=False, sugar=0):  #?params30    """Make coffee with customizable options."""31    order = f"  {size.capitalize()} coffee"32    if milk:33        order += " with milk"34    if sugar > 0:35        order += f", {sugar} sugar(s)"36    print(order)3738#@var=_,!39def print_report(title="Report", columns=2, show_header=False):40    """Print a configurable report."""41    if show_header:42        print(f"  === {title} ===")43    else:44        print(f"  {title}")45    print(f"  ({columns2} columns)")46#@var=_,!
    output  (2 columns)

  17. main()

    48if __name__ == "__main__":49    main()50#@help alldefault

  1. def main():

    1def main():2    print("=== Multiple Default Arguments ===\n")3    4    # Using all defaults5    print("All defaults:")6    make_coffee()
    output=== Multiple Default Arguments ===
All defaults:

  2. order ← Medium coffee

    pass 1 of 7
    5    print("All defaults:")6    make_coffee()7    8    # Override some9    print("\nCustom orders:")10    make_coffee(size="large")11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "small"18    sugar_count = 219    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(sizemedium="medium", milkFalse=FalseFalse, sugar0=0):29    """Make coffee with customizable options."""30    order→   Medium coffee = f"  {sizemedium.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee)
    output  Medium coffee

Custom orders:
    All 7 passes — pass 1 is the card above
    passsizemilksugarorder
    1mediumFalse0 Medium coffee
    2largeFalse0 Large coffee
    3mediumTrue0 Medium coffee
    4mediumFalse2 Medium coffee
    5smallFalse3 Small coffee
    6smallTrue2 Small coffee
    7smallTrue2 Small coffee

  3. order ← Medium coffee with milk

    pass 1 of 3
    30order = f"  {size.capitalize()} coffee"31if milkTrue:32    order→   Medium coffee with milk += " with milk"33if sugar > 0:
    All 3 passes — pass 1 is the card above
    passorder
    1 Medium coffee → Medium coffee with milk
    2 Small coffee → Small coffee with milk
    3 Small coffee → Small coffee with milk

  4. print(order)

    10    make_coffee(size="large")11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "small"18    sugar_count = 219    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee with milk)
    output  Medium coffee with milk

  5. order ← Medium coffee, 2 sugar(s)

    pass 1 of 4
    32    order += " with milk"33if sugar2 > 0:34    order→   Medium coffee, 2 sugar(s) += f", {sugar2} sugar(s)"35print(order)
    All 4 passes — pass 1 is the card above
    passsugarorder
    12 Medium coffee → Medium coffee, 2 sugar(s)
    23 Small coffee → Small coffee, 3 sugar(s)
    32 Small coffee with milk → Small coffee with milk, 2 sugar(s)
    42 Small coffee with milk → Small coffee with milk, 2 sugar(s)

  6. print(order)

    11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "small"18    sugar_count = 219    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee, 2 sugar(s))
    output  Medium coffee, 2 sugar(s)

  7. custom_size ← small, sugar_count ← 2

    12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size→ small = "small"18    sugar_count→ 2 = 219    make_coffee(custom_sizesmall, True, sugar_count2)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Small coffee, 3 sugar(s))
    output  Small coffee, 3 sugar(s)

Fully customized:

  8. print(order)

    18    sugar_count = 219    make_coffee(custom_sizesmall, True, sugar_count2)  # positional20    make_coffee(size=custom_sizesmall, milk=True, sugar=sugar_count2)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Small coffee with milk, 2 sugar(s))
    output  Small coffee with milk, 2 sugar(s)

  9. print(order)

    19    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_sizesmall, milk=True, sugar=sugar_count2)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Small coffee with milk, 2 sugar(s))
    output  Small coffee with milk, 2 sugar(s)

=== Configuration Pattern ===

  10. def print_report(title="Report", columns=2, show_header=False):

    pass 1 of 3
    37def print_report(titleReport="Report", columns2=2, show_headerFalse=FalseFalse):38    """Print a configurable report."""39    if show_header:
    All 3 passes — pass 1 is the card above
    passtitlecolumnsshow_header
    1Report2False
    2Sales Report3False
    3Status2True

  11. else:

    pass 1 of 2
    39if show_header:40    print(f"  === {title} ===")41else:42    print(f"  {titleReport}")43print(f"  ({columns} columns)")
    output  Report

  12. print(f" ({columns} columns)")

    23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns2} columns)")
    output  (2 columns)

  13. else:

    pass 2 of 2
    39if show_header:40    print(f"  === {title} ===")41else:42    print(f"  {titleSales Report}")43print(f"  ({columns} columns)")
    output  Sales Report

  14. print(f" ({columns} columns)")

    24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns3} columns)")
    output  (3 columns)

  15. if show_header:

    38"""Print a configurable report."""39if show_headerTrue:40    print(f"  === {titleStatus} ===")41else:
    output  === Status ===

  16. print(f" ({columns} columns)")

    25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns2} columns)")
    output  (2 columns)

  17. main()

    45if __name__ == "__main__":46    main()

  1. def main():

    1def main():2    print("=== Multiple Default Arguments ===\n")3    4    # Using all defaults5    print("All defaults:")6    make_coffee()
    output=== Multiple Default Arguments ===
All defaults:

  2. order ← Medium coffee

    pass 1 of 7
    5    print("All defaults:")6    make_coffee()7    8    # Override some9    print("\nCustom orders:")10    make_coffee(size="large")11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "large"18    sugar_count = 119    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(sizemedium="medium", milkFalse=FalseFalse, sugar0=0):29    """Make coffee with customizable options."""30    order→   Medium coffee = f"  {sizemedium.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee)
    output  Medium coffee

Custom orders:
    All 7 passes — pass 1 is the card above
    passsizemilksugarorder
    1mediumFalse0 Medium coffee
    2largeFalse0 Large coffee
    3mediumTrue0 Medium coffee
    4mediumFalse2 Medium coffee
    5smallFalse3 Small coffee
    6largeTrue1 Large coffee
    7largeTrue1 Large coffee

  3. order ← Medium coffee with milk

    pass 1 of 3
    30order = f"  {size.capitalize()} coffee"31if milkTrue:32    order→   Medium coffee with milk += " with milk"33if sugar > 0:
    All 3 passes — pass 1 is the card above
    passorder
    1 Medium coffee → Medium coffee with milk
    2 Large coffee → Large coffee with milk
    3 Large coffee → Large coffee with milk

  4. print(order)

    10    make_coffee(size="large")11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "large"18    sugar_count = 119    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee with milk)
    output  Medium coffee with milk

  5. order ← Medium coffee, 2 sugar(s)

    pass 1 of 4
    32    order += " with milk"33if sugar2 > 0:34    order→   Medium coffee, 2 sugar(s) += f", {sugar2} sugar(s)"35print(order)
    All 4 passes — pass 1 is the card above
    passsugarorder
    12 Medium coffee → Medium coffee, 2 sugar(s)
    23 Small coffee → Small coffee, 3 sugar(s)
    31 Large coffee with milk → Large coffee with milk, 1 sugar(s)
    41 Large coffee with milk → Large coffee with milk, 1 sugar(s)

  6. print(order)

    11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "large"18    sugar_count = 119    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee, 2 sugar(s))
    output  Medium coffee, 2 sugar(s)

  7. custom_size ← large, sugar_count ← 1

    12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size→ large = "large"18    sugar_count→ 1 = 119    make_coffee(custom_sizelarge, True, sugar_count1)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Small coffee, 3 sugar(s))
    output  Small coffee, 3 sugar(s)

Fully customized:

  8. print(order)

    18    sugar_count = 119    make_coffee(custom_sizelarge, True, sugar_count1)  # positional20    make_coffee(size=custom_sizelarge, milk=True, sugar=sugar_count1)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Large coffee with milk, 1 sugar(s))
    output  Large coffee with milk, 1 sugar(s)

  9. print(order)

    19    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_sizelarge, milk=True, sugar=sugar_count1)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Large coffee with milk, 1 sugar(s))
    output  Large coffee with milk, 1 sugar(s)

=== Configuration Pattern ===

  10. def print_report(title="Report", columns=2, show_header=False):

    pass 1 of 3
    37def print_report(titleReport="Report", columns2=2, show_headerFalse=FalseFalse):38    """Print a configurable report."""39    if show_header:
    All 3 passes — pass 1 is the card above
    passtitlecolumnsshow_header
    1Report2False
    2Sales Report3False
    3Status2True

  11. else:

    pass 1 of 2
    39if show_header:40    print(f"  === {title} ===")41else:42    print(f"  {titleReport}")43print(f"  ({columns} columns)")
    output  Report

  12. print(f" ({columns} columns)")

    23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns2} columns)")
    output  (2 columns)

  13. else:

    pass 2 of 2
    39if show_header:40    print(f"  === {title} ===")41else:42    print(f"  {titleSales Report}")43print(f"  ({columns} columns)")
    output  Sales Report

  14. print(f" ({columns} columns)")

    24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns3} columns)")
    output  (3 columns)

  15. if show_header:

    38"""Print a configurable report."""39if show_headerTrue:40    print(f"  === {titleStatus} ===")41else:
    output  === Status ===

  16. print(f" ({columns} columns)")

    25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns2} columns)")
    output  (2 columns)

  17. main()

    45if __name__ == "__main__":46    main()

  1. def main():

    1def main():2    print("=== Multiple Default Arguments ===\n")3    4    # Using all defaults5    print("All defaults:")6    make_coffee()
    output=== Multiple Default Arguments ===
All defaults:

  2. order ← Medium coffee

    pass 1 of 7
    5    print("All defaults:")6    make_coffee()7    8    # Override some9    print("\nCustom orders:")10    make_coffee(size="large")11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "large"18    sugar_count = 319    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(sizemedium="medium", milkFalse=FalseFalse, sugar0=0):29    """Make coffee with customizable options."""30    order→   Medium coffee = f"  {sizemedium.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee)
    output  Medium coffee

Custom orders:
    All 7 passes — pass 1 is the card above
    passsizemilksugarorder
    1mediumFalse0 Medium coffee
    2largeFalse0 Large coffee
    3mediumTrue0 Medium coffee
    4mediumFalse2 Medium coffee
    5smallFalse3 Small coffee
    6largeTrue3 Large coffee
    7largeTrue3 Large coffee

  3. order ← Medium coffee with milk

    pass 1 of 3
    30order = f"  {size.capitalize()} coffee"31if milkTrue:32    order→   Medium coffee with milk += " with milk"33if sugar > 0:
    All 3 passes — pass 1 is the card above
    passorder
    1 Medium coffee → Medium coffee with milk
    2 Large coffee → Large coffee with milk
    3 Large coffee → Large coffee with milk

  4. print(order)

    10    make_coffee(size="large")11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "large"18    sugar_count = 319    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee with milk)
    output  Medium coffee with milk

  5. order ← Medium coffee, 2 sugar(s)

    pass 1 of 4
    32    order += " with milk"33if sugar2 > 0:34    order→   Medium coffee, 2 sugar(s) += f", {sugar2} sugar(s)"35print(order)
    All 4 passes — pass 1 is the card above
    passsugarorder
    12 Medium coffee → Medium coffee, 2 sugar(s)
    23 Small coffee → Small coffee, 3 sugar(s)
    33 Large coffee with milk → Large coffee with milk, 3 sugar(s)
    43 Large coffee with milk → Large coffee with milk, 3 sugar(s)

  6. print(order)

    11    make_coffee(milk=True)12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size = "large"18    sugar_count = 319    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Medium coffee, 2 sugar(s))
    output  Medium coffee, 2 sugar(s)

  7. custom_size ← large, sugar_count ← 3

    12    make_coffee(sugar=2)13    make_coffee(size="small", sugar=3)14    15    # Override all16    print("\nFully customized:")17    custom_size→ large = "large"18    sugar_count→ 3 = 319    make_coffee(custom_sizelarge, True, sugar_count3)  # positional20    make_coffee(size=custom_size, milk=True, sugar=sugar_count)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Small coffee, 3 sugar(s))
    output  Small coffee, 3 sugar(s)

Fully customized:

  8. print(order)

    18    sugar_count = 319    make_coffee(custom_sizelarge, True, sugar_count3)  # positional20    make_coffee(size=custom_sizelarge, milk=True, sugar=sugar_count3)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Large coffee with milk, 3 sugar(s))
    output  Large coffee with milk, 3 sugar(s)

  9. print(order)

    19    make_coffee(custom_size, True, sugar_count)  # positional20    make_coffee(size=custom_sizelarge, milk=True, sugar=sugar_count3)  # keyword21    22    # Configuration pattern23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order  Large coffee with milk, 3 sugar(s))
    output  Large coffee with milk, 3 sugar(s)

=== Configuration Pattern ===

  10. def print_report(title="Report", columns=2, show_header=False):

    pass 1 of 3
    37def print_report(titleReport="Report", columns2=2, show_headerFalse=FalseFalse):38    """Print a configurable report."""39    if show_header:
    All 3 passes — pass 1 is the card above
    passtitlecolumnsshow_header
    1Report2False
    2Sales Report3False
    3Status2True

  11. else:

    pass 1 of 2
    39if show_header:40    print(f"  === {title} ===")41else:42    print(f"  {titleReport}")43print(f"  ({columns} columns)")
    output  Report

  12. print(f" ({columns} columns)")

    23    print("\n=== Configuration Pattern ===")24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns2} columns)")
    output  (2 columns)

  13. else:

    pass 2 of 2
    39if show_header:40    print(f"  === {title} ===")41else:42    print(f"  {titleSales Report}")43print(f"  ({columns} columns)")
    output  Sales Report

  14. print(f" ({columns} columns)")

    24    print_report()25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns3} columns)")
    output  (3 columns)

  15. if show_header:

    38"""Print a configurable report."""39if show_headerTrue:40    print(f"  === {titleStatus} ===")41else:
    output  === Status ===

  16. print(f" ({columns} columns)")

    25    print_report(title="Sales Report", columns=3)26    print_report(show_header=True, title="Status")2728def make_coffee(size="medium", milk=False, sugar=0):29    """Make coffee with customizable options."""30    order = f"  {size.capitalize()} coffee"31    if milk:32        order += " with milk"33    if sugar > 0:34        order += f", {sugar} sugar(s)"35    print(order)3637def print_report(title="Report", columns=2, show_header=False):38    """Print a configurable report."""39    if show_header:40        print(f"  === {title} ===")41    else:42        print(f"  {title}")43    print(f"  ({columns2} columns)")
    output  (2 columns)

  17. main()

    45if __name__ == "__main__":46    main()

All defaults must come after non-default parameters.

The mutable default trap

Never use mutable objects as defaults!

mutable_trap.py
Replay: real traced execution (multi-file project)
def main():
    print("=== ⚠️ Mutable Default Trap ===\n")

    # Watch carefully!
    print("Calling add_item 3 times with defaults:")

    result1 = add_item_broken("apple")
    print(f"Call 1: {result1}")

    result2 = add_item_broken("banana")
    print(f"Call 2: {result2}")  # Surprise!

    result3 = add_item_broken("cherry")
    print(f"Call 3: {result3}")  # Even worse!

    print("\n=== What Happened? ===")
    print("Default list is created ONCE at function definition.")
    print("Every call shares the SAME list object!")
    print("Each append adds to that shared list.")

    print("\n=== With Explicit Lists ===")
    # These work because we provide our own lists
    my_list = []
    add_item_broken("dog", my_list)
    print(f"My list: {my_list}")

    other_list = []
    add_item_broken("cat", other_list)
    print(f"Other list: {other_list}")

    print("\n=== Same Problem with Dict ===")
    print(add_settings_broken("theme", "dark"))
    print(add_settings_broken("volume", "100"))  # Both settings!

# ❌ BROKEN: Mutable default
def add_item_broken(item, items=[]):
    items.append(item)
    return items

# ❌ BROKEN: Dict default
def add_settings_broken(key, value, settings={}):
    settings[key] = value
    return settings

if __name__ == "__main__":
    main()

  1. def main():

    1def main():2    print("=== ⚠️ Mutable Default Trap ===\n")3    4    # Watch carefully!  #?trap5    print("Calling add_item 3 times with defaults:")6    7    result1 = add_item_broken("apple")8    print(f"Call 1: {result1}")
    output=== ⚠️ Mutable Default Trap ===
Calling add_item 3 times with defaults:

  2. items ← ['apple']

    pass 1 of 5
    35# ❌ BROKEN: Mutable default  #?broken36def add_item_broken(itemapple, items[]=[]):37    items→ ['apple'].append(itemapple)38    return items['apple']
    All 5 passes — pass 1 is the card above
    passitemitems
    1apple[] → ['apple']
    2banana['apple'] → ['apple', 'banana']
    3cherry['apple', 'banana'] → ['apple', 'banana', 'cherry']
    4dog[] → ['dog']
    5cat[] → ['cat']

  3. result1 ← ['apple']

    7result1→ ['apple'] = add_item_broken("apple")8print(f"Call 1: {result1['apple']}")910result2 = add_item_broken("banana")11print(f"Call 2: {result2}")  # Surprise!
    outputCall 1: ['apple']

  4. result2 ← ['apple', 'banana']

    10result2→ ['apple', 'banana'] = add_item_broken("banana")11print(f"Call 2: {result2['apple', 'banana']}")  # Surprise!1213result3 = add_item_broken("cherry")14print(f"Call 3: {result3}")  # Even worse!
    outputCall 2: ['apple', 'banana']

  5. result3 ← ['apple', 'banana', 'cherry'], my_list ← []

    13result3→ ['apple', 'banana', 'cherry'] = add_item_broken("cherry")14print(f"Call 3: {result3['apple', 'banana', 'cherry']}")  # Even worse!1516print("\n=== What Happened? ===")  #?explain17print("Default list is created ONCE at function definition.")18print("Every call shares the SAME list object!")19print("Each append adds to that shared list.")2021print("\n=== With Explicit Lists ===")22# These work because we provide our own lists23my_list→ [] = []24add_item_broken("dog", my_list[])25print(f"My list: {my_list}")
    outputCall 3: ['apple', 'banana', 'cherry']

=== What Happened? ===
Default list is created ONCE at function definition.
Every call shares the SAME list object!
Each append adds to that shared list.

=== With Explicit Lists ===

  6. my_list ← ['dog'], other_list ← []

    23my_list = []24add_item_broken("dog", my_list→ ['dog'])25print(f"My list: {my_list['dog']}")2627other_list→ [] = []  #?explicit28add_item_broken("cat", other_list[])29print(f"Other list: {other_list}")
    outputMy list: ['dog']

  7. other_list ← ['cat']

    27other_list = []  #?explicit28add_item_broken("cat", other_list→ ['cat'])29print(f"Other list: {other_list['cat']}")3031print("\n=== Same Problem with Dict ===")32print(add_settings_broken("theme", "dark"))33print(add_settings_broken("volume", "100"))  # Both settings!
    outputOther list: ['cat']

=== Same Problem with Dict ===

  8. settings[key] ← dark

    pass 1 of 2
    40# ❌ BROKEN: Dict default41def add_settings_broken(keytheme, valuedark, settings{}={}):42    settings[key]→ dark = valuedark43    return settings{'theme': 'dark'}

  9. print(add_settings_broken("theme", "dark"))

    31print("\n=== Same Problem with Dict ===")32print(add_settings_broken("theme", "dark"))33print(add_settings_broken("volume", "100"))  # Both settings!
    output{'theme': 'dark'}

  10. settings[key] ← 100

    pass 2 of 2
    40# ❌ BROKEN: Dict default41def add_settings_broken(keyvolume, value100, settings{'theme': 'dark'}={}):42    settings[key]→ 100 = value10043    return settings{'theme': 'dark', 'volume': '100'}

  11. print(add_settings_broken("volume", "100")) # Both settings!

    32    print(add_settings_broken("theme", "dark"))33    print(add_settings_broken("volume", "100"))  # Both settings!3435# ❌ BROKEN: Mutable default  #?broken36def add_item_broken(item, items=[]):37    items.append(item)38    return items3940# ❌ BROKEN: Dict default41def add_settings_broken(key, value, settings={}):42    settings[key] = value43    return settings4445if __name__ == "__main__":46    main()47#@help trap
    output{'theme': 'dark', 'volume': '100'}

Defaults are evaluated once at definition time. Mutable defaults persist!

mutable default trap `def f(x=[]):` - the list is created once and reused. Bug waiting to happen.

Use None to avoid the trap

The standard pattern to avoid mutable default issues.

none_pattern.py
Replay: real traced execution (multi-file project)
def main():
    print("=== None Pattern: Safe Defaults ===\n")

    # Correct way with lists
    print("Using None pattern:")

    result1 = add_item("apple")
    print(f"Call 1: {result1}")

    result2 = add_item("banana")
    print(f"Call 2: {result2}")  # Fresh list!

    result3 = add_item("cherry")
    print(f"Call 3: {result3}")  # Still fresh!

    print("\n=== Providing Your Own List ===")
    my_list = ["existing"]
    result = add_item("new", my_list)
    print(f"With my list: {result}")

    print("\n=== Pattern Comparison ===")
    print("❌ def func(items=[]):    - Broken!")
    print("✅ def func(items=None):  - Safe!")

    # Dictionary pattern
    print("\n=== None Pattern with Dict ===")
    config1 = build_config(debug=True)
    print(f"Config 1: {config1}")

    config2 = build_config(verbose=True)
    print(f"Config 2: {config2}")  # Independent!

# ✅ CORRECT: None default
def add_item(item, items=None):
    if items is None:
        items = []  # Fresh list each time!
    items.append(item)
    return items

# ✅ CORRECT: Dict with None
def build_config(base_config=None, **settings):
    if base_config is None:
        base_config = {}  # Fresh dict each time!
    base_config.update(settings)
    return base_config

if __name__ == "__main__":
    main()

  1. def main():

    1#@var=default,withDict2def main():3    print("=== None Pattern: Safe Defaults ===\n")4    5    # Correct way with lists  #?correct6    print("Using None pattern:")7    8    result1 = add_item("apple")9    print(f"Call 1: {result1}")
    output=== None Pattern: Safe Defaults ===
Using None pattern:

  2. def add_item(item, items=None):

    pass 1 of 4
    34# ✅ CORRECT: None default  #?none35def add_item(itemapple, itemsNone=NoneNone):36    if items is None:37        items = []  # Fresh list each time!
    All 4 passes — pass 1 is the card above
    passitemitems
    1appleNone
    2bananaNone
    3cherryNone
    4new['existing'] → ['existing', 'new']

  3. items ← []

    pass 1 of 3
    35def add_item(item, items=None):36    if itemsNone is None:37        items→ [] = []  # Fresh list each time!38    items.append(item)
    All 3 passes — pass 1 is the card above
    passitems
    1None → []
    2None → []
    3None → []

  4. items ← ['apple']

    37    items = []  # Fresh list each time!38items→ ['apple'].append(itemapple)39return items['apple']

  5. result1 ← ['apple']

    8result1→ ['apple'] = add_item("apple")9print(f"Call 1: {result1['apple']}")1011result2 = add_item("banana")12print(f"Call 2: {result2}")  # Fresh list!
    outputCall 1: ['apple']

  6. items ← ['banana']

    37    items = []  # Fresh list each time!38items→ ['banana'].append(itembanana)39return items['banana']

  7. result2 ← ['banana']

    11result2→ ['banana'] = add_item("banana")12print(f"Call 2: {result2['banana']}")  # Fresh list!1314result3 = add_item("cherry")15print(f"Call 3: {result3}")  # Still fresh!
    outputCall 2: ['banana']

  8. items ← ['cherry']

    37    items = []  # Fresh list each time!38items→ ['cherry'].append(itemcherry)39return items['cherry']

  9. result3 ← ['cherry'], my_list ← ['existing']

    14result3→ ['cherry'] = add_item("cherry")15print(f"Call 3: {result3['cherry']}")  # Still fresh!1617print("\n=== Providing Your Own List ===")18my_list→ ['existing'] = ["existing"]  #?provide19result = add_item("new", my_list['existing'])20print(f"With my list: {result}")
    outputCall 3: ['cherry']

=== Providing Your Own List ===

  10. my_list ← ['existing', 'new'], result ← ['existing', 'new']

    18my_list = ["existing"]  #?provide19result→ ['existing', 'new'] = add_item("new", my_list→ ['existing', 'new'])20print(f"With my list: {result['existing', 'new']}")2122print("\n=== Pattern Comparison ===")23print("❌ def func(items=[]):    - Broken!")24print("✅ def func(items=None):  - Safe!")2526# Dictionary pattern  #@var=_,!27print("\n=== None Pattern with Dict ===")28config1 = build_config(debug=True)29print(f"Config 1: {config1}")
    outputWith my list: ['existing', 'new']

=== Pattern Comparison ===
❌ def func(items=[]):    - Broken!
✅ def func(items=None):  - Safe!

=== None Pattern with Dict ===

  11. def build_config(base_config=None, **settings): #?dict

    pass 1 of 2
    42# ✅ CORRECT: Dict with None43def build_config(base_configNone=NoneNone, **settings):  #?dict44    if base_config is None:45        base_config = {}  # Fresh dict each time!

  12. base_config ← {}

    pass 1 of 2
    43def build_config(base_config=None, **settings):  #?dict44    if base_configNone is None:45        base_config→ {} = {}  # Fresh dict each time!46    base_config.update(settings)

  13. base_config ← {'debug': True}

    45        base_config = {}  # Fresh dict each time!46    base_config→ {'debug': True}.update(settings{'debug': True})47    return base_config{'debug': True}48#@var=_,!

  14. config1 ← {'debug': True}

    27print("\n=== None Pattern with Dict ===")28config1→ {'debug': True} = build_config(debug=True)29print(f"Config 1: {config1{'debug': True}}")3031config2 = build_config(verbose=True)32print(f"Config 2: {config2}")  # Independent!
    outputConfig 1: {'debug': True}

  15. def build_config(base_config=None, **settings): #?dict

    pass 2 of 2
    42# ✅ CORRECT: Dict with None43def build_config(base_configNone=NoneNone, **settings):  #?dict44    if base_config is None:45        base_config = {}  # Fresh dict each time!

  16. base_config ← {}

    pass 2 of 2
    43def build_config(base_config=None, **settings):  #?dict44    if base_configNone is None:45        base_config→ {} = {}  # Fresh dict each time!46    base_config.update(settings)

  17. base_config ← {'verbose': True}

    45        base_config = {}  # Fresh dict each time!46    base_config→ {'verbose': True}.update(settings{'verbose': True})47    return base_config{'verbose': True}48#@var=_,!

  18. config2 ← {'verbose': True}

    31    config2→ {'verbose': True} = build_config(verbose=True)32    print(f"Config 2: {config2{'verbose': True}}")  # Independent!3334# ✅ CORRECT: None default  #?none35def add_item(item, items=None):36    if items is None:37        items = []  # Fresh list each time!38    items.append(item)39    return items4041#@var=_,!42# ✅ CORRECT: Dict with None43def build_config(base_config=None, **settings):  #?dict44    if base_config is None:45        base_config = {}  # Fresh dict each time!46    base_config.update(settings)47    return base_config48#@var=_,!4950if __name__ == "__main__":51    main()52#@help correct
    outputConfig 2: {'verbose': True}

Use None as default, then create the mutable object inside the function.

None pattern `def f(x=None): x = x or []` - safe way to have mutable-like defaults.

Exercise: sentinel.py

Explore sentinel objects for distinguishing None from 'not provided'