F-Strings - Python Programming

Creating readable, formatted output is a common programming task. F-strings (formatted string literals) provide the most concise and readable way to embed Python expressions directly in strings. They are faster than older methods and support full Python expressions inside curly braces.

F-strings (formatted string literals) provide a concise way to embed expressions inside string literals using the f prefix and curly braces {}.

Basic Syntax

                            example
                            name = "Alice", age = 25 (default)name = "Maya"name = "Jordan"age = 17age = 42
                        

                            basics.py
                        
Replay: real traced execution (multi-file project)

                            # Basic f-strings


# Simple variable embedding
name = "Alice"
age = 25

# Basic f-string
greeting = f"Hello, {name}!"
print(greeting)

# Multiple variables
message = f"{name} is {age} years old"
print(message)

# Without f-string (for comparison)
old_way = "Hello, " + name + "!"
print("Old way:", old_way)

# Expressions in f-strings
x = 10
y = 20

# Arithmetic
print(f"{x} + {y} = {x + y}")
print(f"{x} * {y} = {x * y}")

# Comparison
print(f"{x} < {y} is {x < y}")

# Function calls
text = "hello"
print(f"Uppercase: {text.upper()}")
print(f"Length: {len(text)}")

# Different data types
name = "Bob"
age = 30
height = 1.75
is_active = True

print(f"Name: {name}")
print(f"Age: {age}")
print(f"Height: {height}m")
print(f"Active: {is_active}")

# Multi-line f-strings
item = "Widget"
price = 19.99
quantity = 5

description = f"""
Product: {item}
Price: ${price}
Quantity: {quantity}
Total: ${price * quantity}
"""
print(description)

# Basic f-strings


# Simple variable embedding
name = "Maya"
age = 25

# Basic f-string
greeting = f"Hello, {name}!"
print(greeting)

# Multiple variables
message = f"{name} is {age} years old"
print(message)

# Without f-string (for comparison)
old_way = "Hello, " + name + "!"
print("Old way:", old_way)

# Expressions in f-strings
x = 10
y = 20

# Arithmetic
print(f"{x} + {y} = {x + y}")
print(f"{x} * {y} = {x * y}")

# Comparison
print(f"{x} < {y} is {x < y}")

# Function calls
text = "hello"
print(f"Uppercase: {text.upper()}")
print(f"Length: {len(text)}")

# Different data types
name = "Bob"
age = 30
height = 1.75
is_active = True

print(f"Name: {name}")
print(f"Age: {age}")
print(f"Height: {height}m")
print(f"Active: {is_active}")

# Multi-line f-strings
item = "Widget"
price = 19.99
quantity = 5

description = f"""
Product: {item}
Price: ${price}
Quantity: {quantity}
Total: ${price * quantity}
"""
print(description)

# Basic f-strings


# Simple variable embedding
name = "Jordan"
age = 25

# Basic f-string
greeting = f"Hello, {name}!"
print(greeting)

# Multiple variables
message = f"{name} is {age} years old"
print(message)

# Without f-string (for comparison)
old_way = "Hello, " + name + "!"
print("Old way:", old_way)

# Expressions in f-strings
x = 10
y = 20

# Arithmetic
print(f"{x} + {y} = {x + y}")
print(f"{x} * {y} = {x * y}")

# Comparison
print(f"{x} < {y} is {x < y}")

# Function calls
text = "hello"
print(f"Uppercase: {text.upper()}")
print(f"Length: {len(text)}")

# Different data types
name = "Bob"
age = 30
height = 1.75
is_active = True

print(f"Name: {name}")
print(f"Age: {age}")
print(f"Height: {height}m")
print(f"Active: {is_active}")

# Multi-line f-strings
item = "Widget"
price = 19.99
quantity = 5

description = f"""
Product: {item}
Price: ${price}
Quantity: {quantity}
Total: ${price * quantity}
"""
print(description)

# Basic f-strings


# Simple variable embedding
name = "Alice"
age = 17

# Basic f-string
greeting = f"Hello, {name}!"
print(greeting)

# Multiple variables
message = f"{name} is {age} years old"
print(message)

# Without f-string (for comparison)
old_way = "Hello, " + name + "!"
print("Old way:", old_way)

# Expressions in f-strings
x = 10
y = 20

# Arithmetic
print(f"{x} + {y} = {x + y}")
print(f"{x} * {y} = {x * y}")

# Comparison
print(f"{x} < {y} is {x < y}")

# Function calls
text = "hello"
print(f"Uppercase: {text.upper()}")
print(f"Length: {len(text)}")

# Different data types
name = "Bob"
age = 30
height = 1.75
is_active = True

print(f"Name: {name}")
print(f"Age: {age}")
print(f"Height: {height}m")
print(f"Active: {is_active}")

# Multi-line f-strings
item = "Widget"
price = 19.99
quantity = 5

description = f"""
Product: {item}
Price: ${price}
Quantity: {quantity}
Total: ${price * quantity}
"""
print(description)

# Basic f-strings


# Simple variable embedding
name = "Alice"
age = 42

# Basic f-string
greeting = f"Hello, {name}!"
print(greeting)

# Multiple variables
message = f"{name} is {age} years old"
print(message)

# Without f-string (for comparison)
old_way = "Hello, " + name + "!"
print("Old way:", old_way)

# Expressions in f-strings
x = 10
y = 20

# Arithmetic
print(f"{x} + {y} = {x + y}")
print(f"{x} * {y} = {x * y}")

# Comparison
print(f"{x} < {y} is {x < y}")

# Function calls
text = "hello"
print(f"Uppercase: {text.upper()}")
print(f"Length: {len(text)}")

# Different data types
name = "Bob"
age = 30
height = 1.75
is_active = True

print(f"Name: {name}")
print(f"Age: {age}")
print(f"Height: {height}m")
print(f"Active: {is_active}")

# Multi-line f-strings
item = "Widget"
price = 19.99
quantity = 5

description = f"""
Product: {item}
Price: ${price}
Quantity: {quantity}
Total: ${price * quantity}
"""
print(description)


                        
1name ← Alice, age ← 25, greeting ← Hello, Alice!, message ← Alice is 25 years old⋯4# Simple variable embedding5name→ Alice = "Alice"6#@name="Maya", "Jordan"7age→ 25 = 258#@age=17, 42910# Basic f-string11greeting→ Hello, Alice! = f"Hello, {nameAlice}!"12print(greetingHello, Alice!)1314# Multiple variables15message→ Alice is 25 years old = f"{nameAlice} is {age25} years old"16print(messageAlice is 25 years old)1718# Without f-string (for comparison)19old_way→ Hello, Alice! = "Hello, " + nameAlice + "!"20print("Old way:", old_wayHello, Alice!)2122# Expressions in f-strings23x→ 10 = 1024y→ 20 = 202526# Arithmetic27print(f"{x10} + {y20} = {x + y}")28print(f"{x10} * {y20} = {x * y}")2930# Comparison31print(f"{x10} < {y20} is {x < y}")3233# Function calls34text→ hello = "hello"35print(f"Uppercase: {texthello.upper()}")36print(f"Length: {len(texthello)}")3738# Different data types39name→ Bob = "Bob"40age→ 30 = 3041height→ 1.75 = 1.7542is_active→ True = True4344print(f"Name: {nameBob}")45print(f"Age: {age30}")46print(f"Height: {height1.75}m")47print(f"Active: {is_activeTrue}")4849# Multi-line f-strings50item→ Widget = "Widget"51price→ 19.99 = 19.9952quantity→ 5 = 55354description→
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
 = f"""55Product: {itemWidget}56Price: ${price19.99}57Quantity: {quantity5}58Total: ${price19.99 * quantity5}59"""60print(description
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
)⋯outputHello, Alice!
Alice is 25 years old
Old way: Hello, Alice!
10 + 20 = 30
10 * 20 = 200
10 < 20 is True
Uppercase: HELLO
Length: 5
Name: Bob
Age: 30
Height: 1.75m
Active: True

Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
1name ← Maya, age ← 25, greeting ← Hello, Maya!, message ← Maya is 25 years old⋯4# Simple variable embedding5name→ Maya = "Maya"6age→ 25 = 2578# Basic f-string9greeting→ Hello, Maya! = f"Hello, {nameMaya}!"10print(greetingHello, Maya!)1112# Multiple variables13message→ Maya is 25 years old = f"{nameMaya} is {age25} years old"14print(messageMaya is 25 years old)1516# Without f-string (for comparison)17old_way→ Hello, Maya! = "Hello, " + nameMaya + "!"18print("Old way:", old_wayHello, Maya!)1920# Expressions in f-strings21x→ 10 = 1022y→ 20 = 202324# Arithmetic25print(f"{x10} + {y20} = {x + y}")26print(f"{x10} * {y20} = {x * y}")2728# Comparison29print(f"{x10} < {y20} is {x < y}")3031# Function calls32text→ hello = "hello"33print(f"Uppercase: {texthello.upper()}")34print(f"Length: {len(texthello)}")3536# Different data types37name→ Bob = "Bob"38age→ 30 = 3039height→ 1.75 = 1.7540is_active→ True = True4142print(f"Name: {nameBob}")43print(f"Age: {age30}")44print(f"Height: {height1.75}m")45print(f"Active: {is_activeTrue}")4647# Multi-line f-strings48item→ Widget = "Widget"49price→ 19.99 = 19.9950quantity→ 5 = 55152description→
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
 = f"""53Product: {itemWidget}54Price: ${price19.99}55Quantity: {quantity5}56Total: ${price19.99 * quantity5}57"""58print(description
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
)⋯outputHello, Maya!
Maya is 25 years old
Old way: Hello, Maya!
10 + 20 = 30
10 * 20 = 200
10 < 20 is True
Uppercase: HELLO
Length: 5
Name: Bob
Age: 30
Height: 1.75m
Active: True

Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
1name ← Jordan, age ← 25, greeting ← Hello, Jordan!, message ← Jordan is 25 years old⋯4# Simple variable embedding5name→ Jordan = "Jordan"6age→ 25 = 2578# Basic f-string9greeting→ Hello, Jordan! = f"Hello, {nameJordan}!"10print(greetingHello, Jordan!)1112# Multiple variables13message→ Jordan is 25 years old = f"{nameJordan} is {age25} years old"14print(messageJordan is 25 years old)1516# Without f-string (for comparison)17old_way→ Hello, Jordan! = "Hello, " + nameJordan + "!"18print("Old way:", old_wayHello, Jordan!)1920# Expressions in f-strings21x→ 10 = 1022y→ 20 = 202324# Arithmetic25print(f"{x10} + {y20} = {x + y}")26print(f"{x10} * {y20} = {x * y}")2728# Comparison29print(f"{x10} < {y20} is {x < y}")3031# Function calls32text→ hello = "hello"33print(f"Uppercase: {texthello.upper()}")34print(f"Length: {len(texthello)}")3536# Different data types37name→ Bob = "Bob"38age→ 30 = 3039height→ 1.75 = 1.7540is_active→ True = True4142print(f"Name: {nameBob}")43print(f"Age: {age30}")44print(f"Height: {height1.75}m")45print(f"Active: {is_activeTrue}")4647# Multi-line f-strings48item→ Widget = "Widget"49price→ 19.99 = 19.9950quantity→ 5 = 55152description→
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
 = f"""53Product: {itemWidget}54Price: ${price19.99}55Quantity: {quantity5}56Total: ${price19.99 * quantity5}57"""58print(description
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
)⋯outputHello, Jordan!
Jordan is 25 years old
Old way: Hello, Jordan!
10 + 20 = 30
10 * 20 = 200
10 < 20 is True
Uppercase: HELLO
Length: 5
Name: Bob
Age: 30
Height: 1.75m
Active: True

Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
1name ← Alice, age ← 17, greeting ← Hello, Alice!, message ← Alice is 17 years old⋯4# Simple variable embedding5name→ Alice = "Alice"6age→ 17 = 1778# Basic f-string9greeting→ Hello, Alice! = f"Hello, {nameAlice}!"10print(greetingHello, Alice!)1112# Multiple variables13message→ Alice is 17 years old = f"{nameAlice} is {age17} years old"14print(messageAlice is 17 years old)1516# Without f-string (for comparison)17old_way→ Hello, Alice! = "Hello, " + nameAlice + "!"18print("Old way:", old_wayHello, Alice!)1920# Expressions in f-strings21x→ 10 = 1022y→ 20 = 202324# Arithmetic25print(f"{x10} + {y20} = {x + y}")26print(f"{x10} * {y20} = {x * y}")2728# Comparison29print(f"{x10} < {y20} is {x < y}")3031# Function calls32text→ hello = "hello"33print(f"Uppercase: {texthello.upper()}")34print(f"Length: {len(texthello)}")3536# Different data types37name→ Bob = "Bob"38age→ 30 = 3039height→ 1.75 = 1.7540is_active→ True = True4142print(f"Name: {nameBob}")43print(f"Age: {age30}")44print(f"Height: {height1.75}m")45print(f"Active: {is_activeTrue}")4647# Multi-line f-strings48item→ Widget = "Widget"49price→ 19.99 = 19.9950quantity→ 5 = 55152description→
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
 = f"""53Product: {itemWidget}54Price: ${price19.99}55Quantity: {quantity5}56Total: ${price19.99 * quantity5}57"""58print(description
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
)⋯outputHello, Alice!
Alice is 17 years old
Old way: Hello, Alice!
10 + 20 = 30
10 * 20 = 200
10 < 20 is True
Uppercase: HELLO
Length: 5
Name: Bob
Age: 30
Height: 1.75m
Active: True

Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
1name ← Alice, age ← 42, greeting ← Hello, Alice!, message ← Alice is 42 years old⋯4# Simple variable embedding5name→ Alice = "Alice"6age→ 42 = 4278# Basic f-string9greeting→ Hello, Alice! = f"Hello, {nameAlice}!"10print(greetingHello, Alice!)1112# Multiple variables13message→ Alice is 42 years old = f"{nameAlice} is {age42} years old"14print(messageAlice is 42 years old)1516# Without f-string (for comparison)17old_way→ Hello, Alice! = "Hello, " + nameAlice + "!"18print("Old way:", old_wayHello, Alice!)1920# Expressions in f-strings21x→ 10 = 1022y→ 20 = 202324# Arithmetic25print(f"{x10} + {y20} = {x + y}")26print(f"{x10} * {y20} = {x * y}")2728# Comparison29print(f"{x10} < {y20} is {x < y}")3031# Function calls32text→ hello = "hello"33print(f"Uppercase: {texthello.upper()}")34print(f"Length: {len(texthello)}")3536# Different data types37name→ Bob = "Bob"38age→ 30 = 3039height→ 1.75 = 1.7540is_active→ True = True4142print(f"Name: {nameBob}")43print(f"Age: {age30}")44print(f"Height: {height1.75}m")45print(f"Active: {is_activeTrue}")4647# Multi-line f-strings48item→ Widget = "Widget"49price→ 19.99 = 19.9950quantity→ 5 = 55152description→
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
 = f"""53Product: {itemWidget}54Price: ${price19.99}55Quantity: {quantity5}56Total: ${price19.99 * quantity5}57"""58print(description
Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999
)⋯outputHello, Alice!
Alice is 42 years old
Old way: Hello, Alice!
10 + 20 = 30
10 * 20 = 200
10 < 20 is True
Uppercase: HELLO
Length: 5
Name: Bob
Age: 30
Height: 1.75m
Active: True

Product: Widget
Price: $19.99
Quantity: 5
Total: $99.94999999999999

fstring_basics Embedding variables and expressions with f-prefix and curly braces

Expressions in F-Strings

                            expressions.py
                        
Replay: real traced execution (multi-file project)

                            # Complex expressions


# Method calls
text = "hello world"

print(f"Original: {text}")
print(f"Upper: {text.upper()}")
print(f"Title: {text.title()}")
print(f"Capitalized: {text.capitalize()}")

# List and dict access
fruits = ["apple", "banana", "cherry"]
person = {"name": "Alice", "age": 25}

print(f"\nFirst fruit: {fruits[0]}")
print(f"Last fruit: {fruits[-1]}")
print(f"Name: {person['name']}")
print(f"Age: {person['age']}")

# Conditional expressions
score = 85

print(f"Result: {score} ({'Pass' if score >= 60 else 'Fail'})")

age = 20
status = f"Status: {'Adult' if age >= 18 else 'Minor'}"
print(status)

# Calculations
price = 19.99
quantity = 5
tax_rate = 0.08

print(f"\nPrice: ${price:.2f}")
print(f"Quantity: {quantity}")
print(f"Subtotal: ${price * quantity:.2f}")
print(f"Tax: ${price * quantity * tax_rate:.2f}")
print(f"Total: ${price * quantity * (1 + tax_rate):.2f}")

# List comprehensions
numbers = [1, 2, 3, 4, 5]

print(f"\nNumbers: {numbers}")
print(f"Squares: {[x**2 for x in numbers]}")
print(f"Sum: {sum(numbers)}")
print(f"Average: {sum(numbers) / len(numbers):.2f}")

# String operations
word1 = "Hello"
word2 = "World"

print(f"\nConcatenated: {word1 + ' ' + word2}")
print(f"Repeated: {word1 * 3}")
print(f"Reversed: {word1[::-1]}")

# Type conversions
value = 42

print(f"\nInteger: {value}")
print(f"Float: {float(value)}")
print(f"String: {str(value)}")
print(f"Binary: {bin(value)}")
print(f"Hex: {hex(value)}")


                        
1text ← hello world, fruits ← ['apple', 'banana', 'cherry'], person ← {'name': 'Alice', 'age': 25}⋯4# Method calls5text→ hello world = "hello world"67print(f"Original: {texthello world}")8print(f"Upper: {texthello world.upper()}")9print(f"Title: {texthello world.title()}")10print(f"Capitalized: {texthello world.capitalize()}")1112# List and dict access13fruits→ ['apple', 'banana', 'cherry'] = ["apple", "banana", "cherry"]14person→ {'name': 'Alice', 'age': 25} = {"name": "Alice", "age": 25}1516print(f"\nFirst fruit: {fruits[0]apple}")17print(f"Last fruit: {fruits[-1]cherry}")18print(f"Name: {person['name']Alice}")19print(f"Age: {person['age']25}")2021# Conditional expressions22score→ 85 = 852324print(f"Result: {score85} ({'Pass' if score >= 60 else 'Fail'})")2526age→ 20 = 2027status→ Status: Adult = f"Status: {'Adult' if age20 >= 18 else 'Minor'}"28print(statusStatus: Adult)2930# Calculations31price→ 19.99 = 19.9932quantity→ 5 = 533tax_rate→ 0.08 = 0.083435print(f"\nPrice: ${price19.99:.2f}")36print(f"Quantity: {quantity5}")37print(f"Subtotal: ${price19.99 * quantity5:.2f}")38print(f"Tax: ${price19.99 * quantity5 * tax_rate0.08:.2f}")39print(f"Total: ${price19.99 * quantity5 * (1 + tax_rate0.08):.2f}")4041# List comprehensions42numbers→ [1, 2, 3, 4, 5] = [1, 2, 3, 4, 5]4344print(f"\nNumbers: {numbers[1, 2, 3, 4, 5]}")45print(f"Squares: {[x**2 for x in numbers[1, 2, 3, 4, 5]]}")46print(f"Sum: {sum(numbers[1, 2, 3, 4, 5])}")47print(f"Average: {sum(numbers[1, 2, 3, 4, 5]) / len(numbers):.2f}")4849# String operations50word1→ Hello = "Hello"51word2→ World = "World"5253print(f"\nConcatenated: {word1Hello + ' ' + word2World}")54print(f"Repeated: {word1Hello * 3}")55print(f"Reversed: {word1[::-1]olleH}")5657# Type conversions58value→ 42 = 425960print(f"\nInteger: {value42}")61print(f"Float: {float(value42)}")62print(f"String: {str(value42)}")63print(f"Binary: {bin(value42)}")64print(f"Hex: {hex(value42)}")⋯outputOriginal: hello world
Upper: HELLO WORLD
Title: Hello World
Capitalized: Hello world

First fruit: apple
Last fruit: cherry
Name: Alice
Age: 25
Result: 85 (Pass)
Status: Adult

Price: $19.99
Quantity: 5
Subtotal: $99.95
Tax: $8.00
Total: $107.95

Numbers: [1, 2, 3, 4, 5]
Squares: [1, 4, 9, 16, 25]
Sum: 15
Average: 3.00

Concatenated: Hello World
Repeated: HelloHelloHello
Reversed: olleH

Integer: 42
Float: 42.0
String: 42
Binary: 0b101010
Hex: 0x2a

fstring_expressions Using method calls, conditionals, and calculations inside f-strings

Format Specifiers

                            format_specs.py
                        
Replay: real traced execution (multi-file project)

                            # Format specifiers


# Decimal places
pi = 3.14159265359

print(f"Default: {pi}")
print(f"2 decimals: {pi:.2f}")
print(f"4 decimals: {pi:.4f}")
print(f"0 decimals: {pi:.0f}")

# Width and alignment
name = "Alice"
short = "Hi"

# Minimum width
print(f"|{name:10}|")  # Right align (default for numbers)
print(f"|{short:10}|")

# Left align with <
print(f"|{name:<10}|")
print(f"|{short:<10}|")

# Right align with >
print(f"|{name:>10}|")
print(f"|{short:>10}|")

# Center align with ^
print(f"|{name:^10}|")
print(f"|{short:^10}|")

# Numbers with width
value = 42

print(f"|{value:5}|")     # Right align
print(f"|{value:<5}|")    # Left align
print(f"|{value:>5}|")    # Right align explicit
print(f"|{value:05}|")    # Zero padding

# Thousands separator
large = 1234567890
price = 1234.56

print(f"With separator: {large:,}")
print(f"Price: ${price:,.2f}")

# Signs
positive = 42
negative = -42

print(f"Default positive: {positive}")
print(f"Always sign: {positive:+}")
print(f"Always sign negative: {negative:+}")
print(f"Space for positive: {positive: }")

# Percentages
ratio = 0.756

print(f"Decimal: {ratio}")
print(f"Percentage: {ratio:.1%}")
print(f"Percentage 2 decimals: {ratio:.2%}")


                        
1pi ← 3.14159265359, name ← Alice, short ← Hi, value ← 42, large ← 1234567890⋯4# Decimal places5pi→ 3.14159265359 = 3.1415926535967print(f"Default: {pi3.14159265359}")8print(f"2 decimals: {pi3.14159265359:.2f}")9print(f"4 decimals: {pi3.14159265359:.4f}")10print(f"0 decimals: {pi3.14159265359:.0f}")1112# Width and alignment13name→ Alice = "Alice"14short→ Hi = "Hi"1516# Minimum width17print(f"|{nameAlice:10}|")  # Right align (default for numbers)18print(f"|{shortHi:10}|")1920# Left align with <21print(f"|{nameAlice:<10}|")22print(f"|{shortHi:<10}|")2324# Right align with >25print(f"|{nameAlice:>10}|")26print(f"|{shortHi:>10}|")2728# Center align with ^29print(f"|{nameAlice:^10}|")30print(f"|{shortHi:^10}|")3132# Numbers with width33value→ 42 = 423435print(f"|{value42:5}|")     # Right align36print(f"|{value42:<5}|")    # Left align37print(f"|{value42:>5}|")    # Right align explicit38print(f"|{value42:05}|")    # Zero padding3940# Thousands separator41large→ 1234567890 = 123456789042price→ 1234.56 = 1234.564344print(f"With separator: {large1234567890:,}")45print(f"Price: ${price1234.56:,.2f}")4647# Signs48positive→ 42 = 4249negative→ -42 = -425051print(f"Default positive: {positive42}")52print(f"Always sign: {positive42:+}")53print(f"Always sign negative: {negative-42:+}")54print(f"Space for positive: {positive42: }")5556# Percentages57ratio→ 0.756 = 0.7565859print(f"Decimal: {ratio0.756}")60print(f"Percentage: {ratio0.756:.1%}")61print(f"Percentage 2 decimals: {ratio0.756:.2%}")⋯outputDefault: 3.14159265359
2 decimals: 3.14
4 decimals: 3.1416
0 decimals: 3
|Alice     |
|Hi        |
|Alice     |
|Hi        |
|     Alice|
|        Hi|
|  Alice   |
|    Hi    |
|   42|
|42   |
|   42|
|00042|
With separator: 1,234,567,890
Price: $1,234.56
Default positive: 42
Always sign: +42
Always sign negative: -42
Space for positive:  42
Decimal: 0.756
Percentage: 75.6%
Percentage 2 decimals: 75.60%

format_specs Controlling decimal places, width, alignment, and number formatting

Alignment

                            alignment.py
                        
Replay: real traced execution (multi-file project)

                            # Alignment and padding


# Table formatting
print("Employee Table:")
print(f"{'Name':<10} {'Age':>5} {'Salary':>10}")
print("-" * 27)

employees = [
    ("Alice", 25, 75000),
    ("Bob", 30, 82000),
    ("Charlie", 35, 91000),
]

for name, age, salary in employees:
    print(f"{name:<10} {age:>5} ${salary:>9,}")

# Padding with different characters
title = "Report"

print(f"\n{title:=^30}")  # Center with = padding
print(f"{title:-^30}")  # Center with - padding
print(f"{title:*^30}")  # Center with * padding

# Right-aligned numbers
print("\nSales Report:")
print(f"{'Item':<15} {'Quantity':>10} {'Revenue':>12}")
print("-" * 40)

sales = [
    ("Widget A", 150, 15000.50),
    ("Widget B", 75, 7500.25),
    ("Widget C", 220, 22000.00),
]

for item, qty, revenue in sales:
    print(f"{item:<15} {qty:>10,} ${revenue:>11,.2f}")

# Progress bar
def progress_bar(percent, width=30):
    """Create a text progress bar"""
    filled = int(width * percent / 100)
    bar = "█" * filled + "░" * (width - filled)
    return f"[{bar}] {percent:>3}%"


print("\nProgress:")
for p in [0, 25, 50, 75, 100]:
    print(progress_bar(p))

# Box drawing
def print_box(text, width=40):
    """Print text in a box"""
    print("┌" + "─" * (width - 2) + "┐")
    print(f"│{text:^{width - 2}}│")
    print("└" + "─" * (width - 2) + "┘")


print()
print_box("Important Message")
print_box("Centered Text", 30)


                        
1employees ← [('Alice', 25, 75000), ('Bob', 30, 82000), ('Charlie', 35, 91000)]⋯4# Table formatting5print("Employee Table:")6print(f"{'Name':<10} {'Age':>5} {'Salary':>10}")7print("-" * 27)89employees→ [('Alice', 25, 75000), ('Bob', 30, 82000), ('Charlie', 35, 91000)] = [10    ("Alice", 25, 75000),11    ("Bob", 30, 82000),12    ("Charlie", 35, 91000),13]⋯outputEmployee Table:
Name         Age     Salary
---------------------------
2for name, age, salary in employees:pass 1 of 3⋯15for nameAlice, age25, salary75000 in employees[('Alice', 25, 75000), ('Bob', 30, 82000), ('Charlie', 35, 91000)]:16    print(f"{nameAlice:<10} {age25:>5} ${salary75000:>9,}")⋯outputAlice         25 $   75,000All 3 passes — pass 1 is the card abovepassnameagesalary
1Alice2575000
2Bob3082000
3Charlie3591000
3title ← Report, sales ← [('Widget A', 150, 15000.5), ('Widget B', 75, 7500.25), ('Widget C', 220, 22000.0)]⋯18# Padding with different characters19title→ Report = "Report"2021print(f"\n{titleReport:=^30}")  # Center with = padding22print(f"{titleReport:-^30}")  # Center with - padding23print(f"{titleReport:*^30}")  # Center with * padding2425# Right-aligned numbers26print("\nSales Report:")27print(f"{'Item':<15} {'Quantity':>10} {'Revenue':>12}")28print("-" * 40)2930sales→ [('Widget A', 150, 15000.5), ('Widget B', 75, 7500.25), ('Widget C', 220, 22000.0)] = [31    ("Widget A", 150, 15000.50),32    ("Widget B", 75, 7500.25),33    ("Widget C", 220, 22000.00),34]⋯output
============Report============
------------Report------------
************Report************

Sales Report:
Item              Quantity      Revenue
----------------------------------------
4for item, qty, revenue in sales:pass 1 of 3⋯36for itemWidget A, qty150, revenue15000.5 in sales[('Widget A', 150, 15000.5), ('Widget B', 75, 7500.25), ('Widget C', 220, 22000.0)]:37    print(f"{itemWidget A:<15} {qty150:>10,} ${revenue15000.5:>11,.2f}")⋯outputWidget A               150 $  15,000.50All 3 passes — pass 1 is the card abovepassitemqtyrevenue
1Widget A15015000.5
2Widget B757500.25
3Widget C22022000.0
5print(" Progress:")⋯47print("\nProgress:")48for p in [0, 25, 50, 75, 100]:⋯output
Progress:
6for p in [0, 25, 50, 75, 100]:pass 1 of 5⋯47print("\nProgress:")48for p0 in [0, 25, 50, 75, 100]:49    print(progress_bar(p0))⋯All 5 passes — pass 1 is the card abovepassp
10
225
350
475
5100
7filled ← 0, bar ← ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░pass 1 of 5⋯39# Progress bar40def progress_bar(percent0, width30=30):41    """Create a text progress bar"""42    filled→ 0 = int(width30 * percent0 / 100)43    bar→ ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░ = "█" * filled0 + "░" * (width30 - filled)44    return f"[{bar░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░}] {percent0:>3}%"⋯All 5 passes — pass 1 is the card abovepasspercentfilledbar
100░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
2257███████░░░░░░░░░░░░░░░░░░░░░░░
35015███████████████░░░░░░░░░░░░░░░
47522██████████████████████░░░░░░░░
510030██████████████████████████████
8print(progress_bar(p))⋯48for p in [0, 25, 50, 75, 100]:49    print(progress_bar(p0))⋯output[░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░]   0%
9print(progress_bar(p))⋯48for p in [0, 25, 50, 75, 100]:49    print(progress_bar(p25))⋯output[███████░░░░░░░░░░░░░░░░░░░░░░░]  25%
10print(progress_bar(p))⋯48for p in [0, 25, 50, 75, 100]:49    print(progress_bar(p50))⋯output[███████████████░░░░░░░░░░░░░░░]  50%
11print(progress_bar(p))⋯48for p in [0, 25, 50, 75, 100]:49    print(progress_bar(p75))⋯output[██████████████████████░░░░░░░░]  75%
12print(progress_bar(p))⋯48for p in [0, 25, 50, 75, 100]:49    print(progress_bar(p100))⋯output[██████████████████████████████] 100%
13print()⋯59print()60print_box("Important Message")61print_box("Centered Text", 30)⋯
14def print_box(text, width=40):pass 1 of 2⋯51# Box drawing52def print_box(textImportant Message, width40=40):53    """Print text in a box"""54    print("┌" + "─" * (width40 - 2) + "┐")55    print(f"│{textImportant Message:^{width40 - 2}}│")56    print("└" + "─" * (width40 - 2) + "┘")⋯output┌──────────────────────────────────────┐
│          Important Message           │
└──────────────────────────────────────┘
15print_box("Important Message")⋯59print()60print_box("Important Message")61print_box("Centered Text", 30)⋯
16def print_box(text, width=40):pass 2 of 2⋯51# Box drawing52def print_box(textCentered Text, width30=40):53    """Print text in a box"""54    print("┌" + "─" * (width30 - 2) + "┐")55    print(f"│{textCentered Text:^{width30 - 2}}│")56    print("└" + "─" * (width30 - 2) + "┘")⋯output┌────────────────────────────┐
│       Centered Text        │
└────────────────────────────┘
17print_box("Centered Text", 30)⋯60print_box("Important Message")61print_box("Centered Text", 30)⋯

All 3 passes — pass 1 is the card above
pass	`name`	`age`	`salary`
1	Alice	25	75000
2	Bob	30	82000
3	Charlie	35	91000

All 3 passes — pass 1 is the card above
pass	`item`	`qty`	`revenue`
1	Widget A	150	15000.5
2	Widget B	75	7500.25
3	Widget C	220	22000.0

All 5 passes — pass 1 is the card above
pass	`p`
1	0
2	25
3	50
4	75
5	100

All 5 passes — pass 1 is the card above
pass	`percent`	`filled`	`bar`
1	0	0	░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
2	25	7	███████░░░░░░░░░░░░░░░░░░░░░░░
3	50	15	███████████████░░░░░░░░░░░░░░░
4	75	22	██████████████████████░░░░░░░░
5	100	30	██████████████████████████████

fstring_alignment Left, right, and center alignment with fill characters

Debug Syntax

                            debug.py
                        
Replay: real traced execution (multi-file project)

                            # Debug format (Python 3.8+)


# Debug syntax
x = 42
name = "Alice"

# Regular f-string
print(f"x is {x}")

# Debug format: shows variable name and value
print(f"{x=}")
print(f"{name=}")

# Debugging expressions
a = 10
b = 20

print(f"{a + b=}")
print(f"{a * b=}")
print(f"{a > b=}")

# Method calls in debug
text = "hello"

print(f"{text.upper()=}")
print(f"{len(text)=}")
print(f"{text[::-1]=}")

# Multiple variables
width = 10
height = 20
area = width * height

print(f"{width=}, {height=}, {area=}")

# Complex expressions
numbers = [1, 2, 3, 4, 5]

print(f"{sum(numbers)=}")
print(f"{max(numbers)=}")
print(f"{len(numbers)=}")

# Debugging calculations
price = 19.99
quantity = 5
tax_rate = 0.08

print(f"{price=:.2f}")
print(f"{quantity=}")
print(f"{price * quantity=:.2f}")
print(f"{price * quantity * tax_rate=:.2f}")

# Custom format with debug
value = 3.14159

print(f"{value=}")
print(f"{value=:.2f}")
print(f"{value=:.4f}")


                        
1x ← 42, name ← Alice, a ← 10, b ← 20, text ← hello, width ← 10⋯4# Debug syntax5x→ 42 = 426name→ Alice = "Alice"78# Regular f-string9print(f"x is {x42}")1011# Debug format: shows variable name and value12print(f"{x42=}")13print(f"{nameAlice=}")1415# Debugging expressions16a→ 10 = 1017b→ 20 = 201819print(f"{a10 + b20=}")20print(f"{a10 * b20=}")21print(f"{a10 > b20=}")2223# Method calls in debug24text→ hello = "hello"2526print(f"{texthello.upper()=}")27print(f"{len(texthello)=}")28print(f"{text[::-1]olleh=}")2930# Multiple variables31width→ 10 = 1032height→ 20 = 2033area→ 200 = width10 * height203435print(f"{width10=}, {height20=}, {area200=}")3637# Complex expressions38numbers→ [1, 2, 3, 4, 5] = [1, 2, 3, 4, 5]3940print(f"{sum(numbers[1, 2, 3, 4, 5])=}")41print(f"{max(numbers[1, 2, 3, 4, 5])=}")42print(f"{len(numbers[1, 2, 3, 4, 5])=}")4344# Debugging calculations45price→ 19.99 = 19.9946quantity→ 5 = 547tax_rate→ 0.08 = 0.084849print(f"{price19.99=:.2f}")50print(f"{quantity5=}")51print(f"{price19.99 * quantity5=:.2f}")52print(f"{price19.99 * quantity5 * tax_rate0.08=:.2f}")5354# Custom format with debug55value→ 3.14159 = 3.141595657print(f"{value3.14159=}")58print(f"{value3.14159=:.2f}")59print(f"{value3.14159=:.4f}")⋯outputx is 42
x=42
name='Alice'
a + b=30
a * b=200
a > b=False
text.upper()='HELLO'
len(text)=5
text[::-1]='olleh'
width=10, height=20, area=200
sum(numbers)=15
max(numbers)=5
len(numbers)=5
price=19.99
quantity=5
price * quantity=99.95
price * quantity * tax_rate=8.00
value=3.14159
value=3.14
value=3.1416

debug_syntax Using f'{variable=}' syntax for debugging output

Advantages

Readable: Expression directly in string
Concise: Less code than .format()
Fast: Evaluated at runtime, optimized
Powerful: Full Python expressions

Python 3.6+

F-strings require Python 3.6 or later. For older versions, use:

"text {}".format(value)
"text %s" % value

Exercise: practical.py

Create invoice, log, and statistics formatters using f-strings