Break and Continue - Python Programming

You're scanning a list of 10,000 products for item #4521. Once found, why keep searching? break lets you exit immediately. Or you're processing orders but want to skip cancelled ones - continue jumps to the next iteration.

Find first match (break)

Stop searching once you find what you're looking for.

                            target
                            target = 42 (default)target = 30target = 99
                        

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

                            numbers = [10, 25, 30, 42, 55, 60]
target = 42

found_index = -1
for i, num in enumerate(numbers):
    print(f"Checking index {i}: {num}")
    if num == target:
        found_index = i
        break

if found_index != -1:
    print(f"Found {target} at index {found_index}")
else:
    print(f"{target} not found")

# Without break, would check all elements unnecessarily
# With break, stops at first match

numbers = [10, 25, 30, 42, 55, 60]
target = 30

found_index = -1
for i, num in enumerate(numbers):
    print(f"Checking index {i}: {num}")
    if num == target:
        found_index = i
        break

if found_index != -1:
    print(f"Found {target} at index {found_index}")
else:
    print(f"{target} not found")

# Without break, would check all elements unnecessarily
# With break, stops at first match

numbers = [10, 25, 30, 42, 55, 60]
target = 99

found_index = -1
for i, num in enumerate(numbers):
    print(f"Checking index {i}: {num}")
    if num == target:
        found_index = i
        break

if found_index != -1:
    print(f"Found {target} at index {found_index}")
else:
    print(f"{target} not found")

# Without break, would check all elements unnecessarily
# With break, stops at first match


                        
1numbers ← [10, 25, 30, 42, 55, 60], target ← 42, found_index ← -11numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]2target→ 42 = 42  #@target=30, 9934found_index→ -1 = -15for i, num in enumerate(numbers):⋯
2for i, num in enumerate(numbers):pass 1 of 4⋯4found_index = -15for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):6    print(f"Checking index {i0}: {num10}")7    if num == target:⋯outputChecking index 0: 10All 4 passes — pass 1 is the card abovepassinumtargetfound_index
1010——
2125——
3230——
4342423
3found_index ← 3⋯6print(f"Checking index {i}: {num}")7if num42 == target42:8    found_index→ 3 = i39    break  #?break_exit⋯
4if found_index != -1:⋯11if found_index3 != -1:12    print(f"Found {target42} at index {found_index3}")13else:⋯outputFound 42 at index 3
1numbers ← [10, 25, 30, 42, 55, 60], target ← 30, found_index ← -11numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]2target→ 30 = 3034found_index→ -1 = -15for i, num in enumerate(numbers):⋯
2for i, num in enumerate(numbers):pass 1 of 3⋯4found_index = -15for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):6    print(f"Checking index {i0}: {num10}")7    if num == target:⋯outputChecking index 0: 10All 3 passes — pass 1 is the card abovepassinumtargetfound_index
1010——
2125——
3230302
3found_index ← 2⋯6print(f"Checking index {i}: {num}")7if num30 == target30:8    found_index→ 2 = i29    break⋯
4if found_index != -1:⋯11if found_index2 != -1:12    print(f"Found {target30} at index {found_index2}")13else:⋯outputFound 30 at index 2
1numbers ← [10, 25, 30, 42, 55, 60], target ← 99, found_index ← -11numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]2target→ 99 = 9934found_index→ -1 = -15for i, num in enumerate(numbers):⋯
2for i, num in enumerate(numbers):pass 1 of 6⋯4found_index = -15for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):6    print(f"Checking index {i0}: {num10}")7    if num == target:⋯outputChecking index 0: 10All 6 passes — pass 1 is the card abovepassinumtarget
1010—
2125—
3230—
4342—
5455—
656099
3else:⋯11if found_index != -1:12    print(f"Found {target} at index {found_index}")13else:14    print(f"{target99} not found")⋯output99 not found

All 4 passes — pass 1 is the card above
pass	`i`	`num`	`target`	`found_index`
1	0	10	—	—
2	1	25	—	—
3	2	30	—	—
4	3	42	42	3

All 3 passes — pass 1 is the card above
pass	`i`	`num`	`target`	`found_index`
1	0	10	—	—
2	1	25	—	—
3	2	30	30	2

All 6 passes — pass 1 is the card above
pass	`i`	`num`	`target`
1	0	10	—
2	1	25	—
3	2	30	—
4	3	42	—
5	4	55	—
6	5	60	99

break exits the loop immediately. More efficient than checking all elements.

break Exit the innermost loop immediately. Loop terminates.

Skip invalid entries (continue)

Skip items that don't meet criteria without stopping the loop.

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

                            scores = [85, -1, 92, 0, 78, -5, 95]  # -1 and -5 are invalid

total = 0
count = 0

print("Processing scores:")
for score in scores:
    if score < 0:
        print(f"  Skipping invalid: {score}")
        continue
    print(f"  Adding: {score}")
    total += score
    count += 1

print(f"Valid scores: {count}")
print(f"Sum: {total}")
if count > 0:
    print(f"Average: {total // count}")

# Pythonic alternative: filter
valid_scores = [s for s in scores if s >= 0]
print(f"\nFiltered: {valid_scores}")
print(f"Average: {sum(valid_scores) // len(valid_scores)}")


                        
1scores ← [85, -1, 92, 0, 78, -5, 95], total ← 0, count ← 01scores→ [85, -1, 92, 0, 78, -5, 95] = [85, -1, 92, 0, 78, -5, 95]  # -1 and -5 are invalid23total→ 0 = 04count→ 0 = 056print("Processing scores:")7for score in scores:⋯outputProcessing scores:
2total ← 85, count ← 1pass 1 of 7⋯6print("Processing scores:")7for score85 in scores[85, -1, 92, 0, 78, -5, 95]:8    if score < 0:  #?skip_invalid9        print(f"  Skipping invalid: {score}")10        continue11    print(f"  Adding: {score85}")12    total→ 85 += score8513    count→ 1 += 1⋯output  Adding: 85All 7 passes — pass 1 is the card abovepassscoretotalcount
1850 → 850 → 1
2-1——
39285 → 1771 → 2
401772 → 3
578177 → 2553 → 4
6-5——
795255 → 3504 → 5
3if score < 0:  #?skip_invalidpass 1 of 2⋯7for score in scores:8    if score-1 < 0:  #?skip_invalid9        print(f"  Skipping invalid: {score-1}")10        continue11    print(f"  Adding: {score}")⋯output  Skipping invalid: -1
4if score < 0:  #?skip_invalidpass 2 of 2⋯7for score in scores:8    if score-5 < 0:  #?skip_invalid9        print(f"  Skipping invalid: {score-5}")10        continue11    print(f"  Adding: {score}")⋯output  Skipping invalid: -5
5print(f"Valid scores: {count}")⋯15print(f"Valid scores: {count5}")16print(f"Sum: {total350}")17if count > 0:⋯outputValid scores: 5
Sum: 350
6if count > 0:⋯16print(f"Sum: {total}")17if count5 > 0:18    print(f"Average: {total350 // count5}")⋯outputAverage: 70
7valid_scores ← [85, 92, 0, 78, 95]⋯20# Pythonic alternative: filter21valid_scores→ [85, 92, 0, 78, 95] = [s for s in scores[85, -1, 92, 0, 78, -5, 95] if s >= 0]22print(f"\nFiltered: {valid_scores[85, 92, 0, 78, 95]}")23print(f"Average: {sum(valid_scores[85, 92, 0, 78, 95]) // len(valid_scores)}")⋯output
Filtered: [85, 92, 0, 78, 95]
Average: 70

All 7 passes — pass 1 is the card above
pass	`score`	`total`	`count`
1	85	0 → 85	0 → 1
2	-1	—	—
3	92	85 → 177	1 → 2
4	0	177	2 → 3
5	78	177 → 255	3 → 4
6	-5	—	—
7	95	255 → 350	4 → 5

continue jumps to the next iteration, skipping the rest of the loop body.

continue Skip rest of current iteration, go to next iteration.

Early exit on error

Stop processing if something goes wrong.

                            commands
                            commands = ["load", "process", "error", "save", "exit"] (default)commands = ["init", "run", "complete"]commands = ["start", "stop"]
                        

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

                            commands = ["load", "process", "error", "save", "exit"]

success = True

for cmd in commands:
    print(f"Executing: {cmd}")

    # Stop on error
    if cmd == "error":
        print("ERROR: Operation failed!")
        success = False
        break

    print("  Done.")

if success:
    print("All commands completed successfully.")
else:
    print("Processing stopped due to error.")
commands = ["init", "run", "complete"]

success = True

for cmd in commands:
    print(f"Executing: {cmd}")

    # Stop on error
    if cmd == "error":
        print("ERROR: Operation failed!")
        success = False
        break

    print("  Done.")

if success:
    print("All commands completed successfully.")
else:
    print("Processing stopped due to error.")
commands = ["start", "stop"]

success = True

for cmd in commands:
    print(f"Executing: {cmd}")

    # Stop on error
    if cmd == "error":
        print("ERROR: Operation failed!")
        success = False
        break

    print("  Done.")

if success:
    print("All commands completed successfully.")
else:
    print("Processing stopped due to error.")

                        
1commands ← ['load', 'process', 'error', 'save', 'exit'], success ← True1commands→ ['load', 'process', 'error', 'save', 'exit'] = ["load", "process", "error", "save", "exit"]2#@commands=["init", "run", "complete"], ["start", "stop"]34success→ True = True⋯
2for cmd in commands:pass 1 of 3⋯6for cmdload in commands['load', 'process', 'error', 'save', 'exit']:7    print(f"Executing: {cmdload}")8    9    # Stop on error10    if cmd == "error":11        print("ERROR: Operation failed!")12        success = False13        break14    15    print("  Done.")⋯outputExecuting: load
  Done.All 3 passes — pass 1 is the card abovepasscmdsuccess
1load—
2process—
3errorFalse
3success ← False⋯9# Stop on error10if cmderror == "error":11    print("ERROR: Operation failed!")12    success→ False = False13    break⋯outputERROR: Operation failed!
4else:⋯17if success:18    print("All commands completed successfully.")19else:20    print("Processing stopped due to error.")⋯outputProcessing stopped due to error.
1commands ← ['init', 'run', 'complete'], success ← True1commands→ ['init', 'run', 'complete'] = ["init", "run", "complete"]23success→ True = True⋯
2for cmd in commands:pass 1 of 3⋯5for cmdinit in commands['init', 'run', 'complete']:6    print(f"Executing: {cmdinit}")7    8    # Stop on error9    if cmd == "error":10        print("ERROR: Operation failed!")11        success = False12        break13    14    print("  Done.")⋯outputExecuting: init
  Done.All 3 passes — pass 1 is the card abovepasscmdsuccess
1init—
2run—
3completeTrue
3if success:⋯16if successTrue:17    print("All commands completed successfully.")18else:⋯outputAll commands completed successfully.
1commands ← ['start', 'stop'], success ← True1commands→ ['start', 'stop'] = ["start", "stop"]23success→ True = True⋯
2for cmd in commands:pass 1 of 2⋯5for cmdstart in commands['start', 'stop']:6    print(f"Executing: {cmdstart}")7    8    # Stop on error9    if cmd == "error":10        print("ERROR: Operation failed!")11        success = False12        break13    14    print("  Done.")⋯outputExecuting: start
  Done.
3for cmd in commands:pass 2 of 2⋯5for cmdstop in commands['start', 'stop']:6    print(f"Executing: {cmdstop}")7    8    # Stop on error9    if cmd == "error":10        print("ERROR: Operation failed!")11        success = False12        break13    14    print("  Done.")⋯outputExecuting: stop
  Done.
4if success:⋯16if successTrue:17    print("All commands completed successfully.")18else:⋯outputAll commands completed successfully.

All 3 passes — pass 1 is the card above
pass	`cmd`	`success`
1	load	—
2	process	—
3	error	False

All 3 passes — pass 1 is the card above
pass	`cmd`	`success`
1	init	—
2	run	—
3	complete	True

Validate early and break if invalid - cleaner than deep nesting.

Process until sentinel

Process data until you encounter a special "stop" value.

                            data
                            data = [10, 20, 30, 40, -1, 50, 60] (default)data = [5, 10, 15, -1, 20]data = [100, 200, 300, 400]
                        

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

                            # Data with sentinel value -1 marking end
data = [10, 20, 30, 40, -1, 50, 60]

print("Processing until sentinel (-1):")
total = 0

for value in data:
    if value == -1:
        print("Sentinel found, stopping.")
        break
    print(f"Processing: {value}")
    total += value

print(f"Sum of processed values: {total}")

# Pythonic: itertools.takewhile
from itertools import takewhile

print("\nUsing takewhile:")
data2 = [10, 20, 30, 40, -1, 50, 60]
for value in takewhile(lambda x: x != -1, data2):
    print(f"Processing: {value}")

total2 = sum(takewhile(lambda x: x != -1, data2))
print(f"Sum: {total2}")

# Data with sentinel value -1 marking end
data = [5, 10, 15, -1, 20]

print("Processing until sentinel (-1):")
total = 0

for value in data:
    if value == -1:
        print("Sentinel found, stopping.")
        break
    print(f"Processing: {value}")
    total += value

print(f"Sum of processed values: {total}")

# Pythonic: itertools.takewhile
from itertools import takewhile

print("\nUsing takewhile:")
data2 = [10, 20, 30, 40, -1, 50, 60]
for value in takewhile(lambda x: x != -1, data2):
    print(f"Processing: {value}")

total2 = sum(takewhile(lambda x: x != -1, data2))
print(f"Sum: {total2}")

# Data with sentinel value -1 marking end
data = [100, 200, 300, 400]

print("Processing until sentinel (-1):")
total = 0

for value in data:
    if value == -1:
        print("Sentinel found, stopping.")
        break
    print(f"Processing: {value}")
    total += value

print(f"Sum of processed values: {total}")

# Pythonic: itertools.takewhile
from itertools import takewhile

print("\nUsing takewhile:")
data2 = [10, 20, 30, 40, -1, 50, 60]
for value in takewhile(lambda x: x != -1, data2):
    print(f"Processing: {value}")

total2 = sum(takewhile(lambda x: x != -1, data2))
print(f"Sum: {total2}")


                        
1data ← [10, 20, 30, 40, -1, 50, 60], total ← 01# Data with sentinel value -1 marking end2data→ [10, 20, 30, 40, -1, 50, 60] = [10, 20, 30, 40, -1, 50, 60]3#@data=[5, 10, 15, -1, 20], [100, 200, 300, 400]45print("Processing until sentinel (-1):")6total→ 0 = 0⋯outputProcessing until sentinel (-1):
2total ← 10pass 1 of 5⋯8for value10 in data[10, 20, 30, 40, -1, 50, 60]:9    if value == -1:  #?sentinel_check10        print("Sentinel found, stopping.")11        break12    print(f"Processing: {value10}")13    total→ 10 += value10⋯outputProcessing: 10All 5 passes — pass 1 is the card abovepassvaluetotal
1100 → 10
22010 → 30
33030 → 60
44060 → 100
5-1—
3if value == -1:  #?sentinel_check⋯8for value in data:9    if value-1 == -1:  #?sentinel_check10        print("Sentinel found, stopping.")11        break12    print(f"Processing: {value}")⋯outputSentinel found, stopping.
4data2 ← [10, 20, 30, 40, -1, 50, 60]⋯15print(f"Sum of processed values: {total100}")1617# Pythonic: itertools.takewhile18from itertools import takewhile1920print("\nUsing takewhile:")21data2→ [10, 20, 30, 40, -1, 50, 60] = [10, 20, 30, 40, -1, 50, 60]22for value in takewhile(lambda x: x != -1, data2):⋯outputSum of processed values: 100

Using takewhile:
5for value in takewhile(lambda x: x != -1, data2):pass 1 of 4⋯21data2 = [10, 20, 30, 40, -1, 50, 60]22for value10 in takewhile(lambda x: x != -1, data2[10, 20, 30, 40, -1, 50, 60]):23    print(f"Processing: {value10}")⋯outputProcessing: 10All 4 passes — pass 1 is the card abovepassvalue
110
220
330
440
6total2 ← 100⋯25total2→ 100 = sum(takewhile(lambda x: x != -1, data2[10, 20, 30, 40, -1, 50, 60]))26print(f"Sum: {total2100}")⋯outputSum: 100
1data ← [5, 10, 15, -1, 20], total ← 01# Data with sentinel value -1 marking end2data→ [5, 10, 15, -1, 20] = [5, 10, 15, -1, 20]34print("Processing until sentinel (-1):")5total→ 0 = 0⋯outputProcessing until sentinel (-1):
2total ← 5pass 1 of 4⋯7for value5 in data[5, 10, 15, -1, 20]:8    if value == -1:9        print("Sentinel found, stopping.")10        break11    print(f"Processing: {value5}")12    total→ 5 += value5⋯outputProcessing: 5All 4 passes — pass 1 is the card abovepassvaluetotal
150 → 5
2105 → 15
31515 → 30
4-1—
3if value == -1:⋯7for value in data:8    if value-1 == -1:9        print("Sentinel found, stopping.")10        break11    print(f"Processing: {value}")⋯outputSentinel found, stopping.
4data2 ← [10, 20, 30, 40, -1, 50, 60]⋯14print(f"Sum of processed values: {total30}")1516# Pythonic: itertools.takewhile17from itertools import takewhile1819print("\nUsing takewhile:")20data2→ [10, 20, 30, 40, -1, 50, 60] = [10, 20, 30, 40, -1, 50, 60]21for value in takewhile(lambda x: x != -1, data2):⋯outputSum of processed values: 30

Using takewhile:
5for value in takewhile(lambda x: x != -1, data2):pass 1 of 4⋯20data2 = [10, 20, 30, 40, -1, 50, 60]21for value10 in takewhile(lambda x: x != -1, data2[10, 20, 30, 40, -1, 50, 60]):22    print(f"Processing: {value10}")⋯outputProcessing: 10All 4 passes — pass 1 is the card abovepassvalue
110
220
330
440
6total2 ← 100⋯24total2→ 100 = sum(takewhile(lambda x: x != -1, data2[10, 20, 30, 40, -1, 50, 60]))25print(f"Sum: {total2100}")⋯outputSum: 100
1data ← [100, 200, 300, 400], total ← 01# Data with sentinel value -1 marking end2data→ [100, 200, 300, 400] = [100, 200, 300, 400]34print("Processing until sentinel (-1):")5total→ 0 = 0⋯outputProcessing until sentinel (-1):
2total ← 100pass 1 of 4⋯7for value100 in data[100, 200, 300, 400]:8    if value == -1:9        print("Sentinel found, stopping.")10        break11    print(f"Processing: {value100}")12    total→ 100 += value100⋯outputProcessing: 100All 4 passes — pass 1 is the card abovepassvaluetotal
11000 → 100
2200100 → 300
3300300 → 600
4400600 → 1000
3data2 ← [10, 20, 30, 40, -1, 50, 60]⋯14print(f"Sum of processed values: {total1000}")1516# Pythonic: itertools.takewhile17from itertools import takewhile1819print("\nUsing takewhile:")20data2→ [10, 20, 30, 40, -1, 50, 60] = [10, 20, 30, 40, -1, 50, 60]21for value in takewhile(lambda x: x != -1, data2):⋯outputSum of processed values: 1000

Using takewhile:
4for value in takewhile(lambda x: x != -1, data2):pass 1 of 4⋯20data2 = [10, 20, 30, 40, -1, 50, 60]21for value10 in takewhile(lambda x: x != -1, data2[10, 20, 30, 40, -1, 50, 60]):22    print(f"Processing: {value10}")⋯outputProcessing: 10All 4 passes — pass 1 is the card abovepassvalue
110
220
330
440
5total2 ← 100⋯24total2→ 100 = sum(takewhile(lambda x: x != -1, data2[10, 20, 30, 40, -1, 50, 60]))25print(f"Sum: {total2100}")⋯outputSum: 100

All 5 passes — pass 1 is the card above
pass	`value`	`total`
1	10	0 → 10
2	20	10 → 30
3	30	30 → 60
4	40	60 → 100
5	-1	—

All 4 passes — pass 1 is the card above
pass	`value`
1	10
2	20
3	30
4	40

All 4 passes — pass 1 is the card above
pass	`value`	`total`
1	5	0 → 5
2	10	5 → 15
3	15	15 → 30
4	-1	—

All 4 passes — pass 1 is the card above
pass	`value`
1	10
2	20
3	30
4	40

All 4 passes — pass 1 is the card above
pass	`value`	`total`
1	100	0 → 100
2	200	100 → 300
3	300	300 → 600
4	400	600 → 1000

All 4 passes — pass 1 is the card above
pass	`value`
1	10
2	20
3	30
4	40

Sentinel values signal "end of data" - common in file and stream processing.

sentinel Special value marking end of data: -1, None, "END", etc.

For-else (Python unique!)

Python's for-else executes else only if loop completes without break.

                            example
                            target = 42, search_id = 2 (default)target = 30target = 99search_id = 1search_id = 99
                        

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

                            # Python's unique for-else construct
numbers = [10, 25, 30, 42, 55, 60]
target = 42

# for-else: else runs only if loop completes WITHOUT break
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        break
else:
    print(f"{target} not found")

# Equivalent without for-else
print("\n--- Without for-else ---")
found = False
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        found = True
        break
if not found:
    print(f"{target} not found")

# Practical: search with validation
print("\n--- Practical example ---")
users = [
    {"id": 1, "name": "Alice", "active": True},
    {"id": 2, "name": "Bob", "active": False},
    {"id": 3, "name": "Charlie", "active": True},
]
search_id = 2

for user in users:
    if user["id"] == search_id:
        print(f"Found user: {user['name']}")
        break
else:
    print(f"User {search_id} not found")

# Python's unique for-else construct
numbers = [10, 25, 30, 42, 55, 60]
target = 30

# for-else: else runs only if loop completes WITHOUT break
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        break
else:
    print(f"{target} not found")

# Equivalent without for-else
print("\n--- Without for-else ---")
found = False
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        found = True
        break
if not found:
    print(f"{target} not found")

# Practical: search with validation
print("\n--- Practical example ---")
users = [
    {"id": 1, "name": "Alice", "active": True},
    {"id": 2, "name": "Bob", "active": False},
    {"id": 3, "name": "Charlie", "active": True},
]
search_id = 2

for user in users:
    if user["id"] == search_id:
        print(f"Found user: {user['name']}")
        break
else:
    print(f"User {search_id} not found")

# Python's unique for-else construct
numbers = [10, 25, 30, 42, 55, 60]
target = 99

# for-else: else runs only if loop completes WITHOUT break
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        break
else:
    print(f"{target} not found")

# Equivalent without for-else
print("\n--- Without for-else ---")
found = False
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        found = True
        break
if not found:
    print(f"{target} not found")

# Practical: search with validation
print("\n--- Practical example ---")
users = [
    {"id": 1, "name": "Alice", "active": True},
    {"id": 2, "name": "Bob", "active": False},
    {"id": 3, "name": "Charlie", "active": True},
]
search_id = 2

for user in users:
    if user["id"] == search_id:
        print(f"Found user: {user['name']}")
        break
else:
    print(f"User {search_id} not found")

# Python's unique for-else construct
numbers = [10, 25, 30, 42, 55, 60]
target = 42

# for-else: else runs only if loop completes WITHOUT break
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        break
else:
    print(f"{target} not found")

# Equivalent without for-else
print("\n--- Without for-else ---")
found = False
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        found = True
        break
if not found:
    print(f"{target} not found")

# Practical: search with validation
print("\n--- Practical example ---")
users = [
    {"id": 1, "name": "Alice", "active": True},
    {"id": 2, "name": "Bob", "active": False},
    {"id": 3, "name": "Charlie", "active": True},
]
search_id = 1

for user in users:
    if user["id"] == search_id:
        print(f"Found user: {user['name']}")
        break
else:
    print(f"User {search_id} not found")

# Python's unique for-else construct
numbers = [10, 25, 30, 42, 55, 60]
target = 42

# for-else: else runs only if loop completes WITHOUT break
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        break
else:
    print(f"{target} not found")

# Equivalent without for-else
print("\n--- Without for-else ---")
found = False
for i, num in enumerate(numbers):
    if num == target:
        print(f"Found {target} at index {i}")
        found = True
        break
if not found:
    print(f"{target} not found")

# Practical: search with validation
print("\n--- Practical example ---")
users = [
    {"id": 1, "name": "Alice", "active": True},
    {"id": 2, "name": "Bob", "active": False},
    {"id": 3, "name": "Charlie", "active": True},
]
search_id = 99

for user in users:
    if user["id"] == search_id:
        print(f"Found user: {user['name']}")
        break
else:
    print(f"User {search_id} not found")


                        
1numbers ← [10, 25, 30, 42, 55, 60], target ← 421# Python's unique for-else construct2numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]3target→ 42 = 42  #@target=30, 99⋯
2for i, num in enumerate(numbers):pass 1 of 4⋯5# for-else: else runs only if loop completes WITHOUT break6for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):7    if num == target:8        print(f"Found {target} at index {i}")⋯All 4 passes — pass 1 is the card abovepassinumtarget
1010—
2125—
3230—
434242
3if num == target:⋯6for i, num in enumerate(numbers):7    if num42 == target42:8        print(f"Found {target42} at index {i3}")9        break10else:  #?for_else⋯outputFound 42 at index 3
4found ← False⋯13# Equivalent without for-else14print("\n--- Without for-else ---")15found→ False = False16for i, num in enumerate(numbers):⋯output
--- Without for-else ---
5for i, num in enumerate(numbers):pass 1 of 4⋯15found = False16for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):17    if num == target:18        print(f"Found {target} at index {i}")⋯All 4 passes — pass 1 is the card abovepassinumtargetfound
1010——
2125——
3230——
434242True
6found ← True⋯16for i, num in enumerate(numbers):17    if num42 == target42:18        print(f"Found {target42} at index {i3}")19        found→ True = True20        break21if not found:⋯outputFound 42 at index 3
7users ← [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]⋯24# Practical: search with validation25print("\n--- Practical example ---")26users→ [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}] = [27    {"id": 1, "name": "Alice", "active": True},28    {"id": 2, "name": "Bob", "active": False},29    {"id": 3, "name": "Charlie", "active": True},30]31search_id→ 2 = 2  #@search_id=1, 99⋯output
--- Practical example ---
8for user in users:pass 1 of 2⋯33for user{'id': 1, 'name': 'Alice', 'active': True} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯
9for user in users:pass 2 of 2⋯33for user{'id': 2, 'name': 'Bob', 'active': False} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯
10if user["id"] == search_id:⋯33for user in users:34    if user["id"]2 == search_id2:35        print(f"Found user: {user['name']Bob}")36        break37else:⋯outputFound user: Bob
1numbers ← [10, 25, 30, 42, 55, 60], target ← 301# Python's unique for-else construct2numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]3target→ 30 = 30⋯
2for i, num in enumerate(numbers):pass 1 of 3⋯5# for-else: else runs only if loop completes WITHOUT break6for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):7    if num == target:8        print(f"Found {target} at index {i}")⋯All 3 passes — pass 1 is the card abovepassinumtarget
1010—
2125—
323030
3if num == target:⋯6for i, num in enumerate(numbers):7    if num30 == target30:8        print(f"Found {target30} at index {i2}")9        break10else:⋯outputFound 30 at index 2
4found ← False⋯13# Equivalent without for-else14print("\n--- Without for-else ---")15found→ False = False16for i, num in enumerate(numbers):⋯output
--- Without for-else ---
5for i, num in enumerate(numbers):pass 1 of 3⋯15found = False16for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):17    if num == target:18        print(f"Found {target} at index {i}")⋯All 3 passes — pass 1 is the card abovepassinumtargetfound
1010——
2125——
323030True
6found ← True⋯16for i, num in enumerate(numbers):17    if num30 == target30:18        print(f"Found {target30} at index {i2}")19        found→ True = True20        break21if not found:⋯outputFound 30 at index 2
7users ← [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]⋯24# Practical: search with validation25print("\n--- Practical example ---")26users→ [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}] = [27    {"id": 1, "name": "Alice", "active": True},28    {"id": 2, "name": "Bob", "active": False},29    {"id": 3, "name": "Charlie", "active": True},30]31search_id→ 2 = 2⋯output
--- Practical example ---
8for user in users:pass 1 of 2⋯33for user{'id': 1, 'name': 'Alice', 'active': True} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯
9for user in users:pass 2 of 2⋯33for user{'id': 2, 'name': 'Bob', 'active': False} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯
10if user["id"] == search_id:⋯33for user in users:34    if user["id"]2 == search_id2:35        print(f"Found user: {user['name']Bob}")36        break37else:⋯outputFound user: Bob
1numbers ← [10, 25, 30, 42, 55, 60], target ← 991# Python's unique for-else construct2numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]3target→ 99 = 99⋯
2for i, num in enumerate(numbers):pass 1 of 6⋯5# for-else: else runs only if loop completes WITHOUT break6for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):7    if num == target:8        print(f"Found {target} at index {i}")⋯All 6 passes — pass 1 is the card abovepassinumtarget
1010—
2125—
3230—
4342—
5455—
656099
3else:⋯8        print(f"Found {target} at index {i}")9        break10else:11    print(f"{target99} not found")⋯output99 not found
4found ← False⋯13# Equivalent without for-else14print("\n--- Without for-else ---")15found→ False = False16for i, num in enumerate(numbers):⋯output
--- Without for-else ---
5for i, num in enumerate(numbers):pass 1 of 6⋯15found = False16for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):17    if num == target:18        print(f"Found {target} at index {i}")⋯All 6 passes — pass 1 is the card abovepassinumfoundtarget
1010——
2125——
3230——
4342——
5455——
6560False99
6if not found:⋯20        break21if not foundFalse:22    print(f"{target99} not found")⋯output99 not found
7users ← [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]⋯24# Practical: search with validation25print("\n--- Practical example ---")26users→ [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}] = [27    {"id": 1, "name": "Alice", "active": True},28    {"id": 2, "name": "Bob", "active": False},29    {"id": 3, "name": "Charlie", "active": True},30]31search_id→ 2 = 2⋯output
--- Practical example ---
8for user in users:pass 1 of 2⋯33for user{'id': 1, 'name': 'Alice', 'active': True} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯
9for user in users:pass 2 of 2⋯33for user{'id': 2, 'name': 'Bob', 'active': False} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯
10if user["id"] == search_id:⋯33for user in users:34    if user["id"]2 == search_id2:35        print(f"Found user: {user['name']Bob}")36        break37else:⋯outputFound user: Bob
1numbers ← [10, 25, 30, 42, 55, 60], target ← 421# Python's unique for-else construct2numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]3target→ 42 = 42⋯
2for i, num in enumerate(numbers):pass 1 of 4⋯5# for-else: else runs only if loop completes WITHOUT break6for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):7    if num == target:8        print(f"Found {target} at index {i}")⋯All 4 passes — pass 1 is the card abovepassinumtarget
1010—
2125—
3230—
434242
3if num == target:⋯6for i, num in enumerate(numbers):7    if num42 == target42:8        print(f"Found {target42} at index {i3}")9        break10else:⋯outputFound 42 at index 3
4found ← False⋯13# Equivalent without for-else14print("\n--- Without for-else ---")15found→ False = False16for i, num in enumerate(numbers):⋯output
--- Without for-else ---
5for i, num in enumerate(numbers):pass 1 of 4⋯15found = False16for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):17    if num == target:18        print(f"Found {target} at index {i}")⋯All 4 passes — pass 1 is the card abovepassinumtargetfound
1010——
2125——
3230——
434242True
6found ← True⋯16for i, num in enumerate(numbers):17    if num42 == target42:18        print(f"Found {target42} at index {i3}")19        found→ True = True20        break21if not found:⋯outputFound 42 at index 3
7users ← [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]⋯24# Practical: search with validation25print("\n--- Practical example ---")26users→ [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}] = [27    {"id": 1, "name": "Alice", "active": True},28    {"id": 2, "name": "Bob", "active": False},29    {"id": 3, "name": "Charlie", "active": True},30]31search_id→ 1 = 1⋯output
--- Practical example ---
8for user in users:⋯33for user{'id': 1, 'name': 'Alice', 'active': True} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯
9if user["id"] == search_id:⋯33for user in users:34    if user["id"]1 == search_id1:35        print(f"Found user: {user['name']Alice}")36        break37else:⋯outputFound user: Alice
1numbers ← [10, 25, 30, 42, 55, 60], target ← 421# Python's unique for-else construct2numbers→ [10, 25, 30, 42, 55, 60] = [10, 25, 30, 42, 55, 60]3target→ 42 = 42⋯
2for i, num in enumerate(numbers):pass 1 of 4⋯5# for-else: else runs only if loop completes WITHOUT break6for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):7    if num == target:8        print(f"Found {target} at index {i}")⋯All 4 passes — pass 1 is the card abovepassinumtarget
1010—
2125—
3230—
434242
3if num == target:⋯6for i, num in enumerate(numbers):7    if num42 == target42:8        print(f"Found {target42} at index {i3}")9        break10else:⋯outputFound 42 at index 3
4found ← False⋯13# Equivalent without for-else14print("\n--- Without for-else ---")15found→ False = False16for i, num in enumerate(numbers):⋯output
--- Without for-else ---
5for i, num in enumerate(numbers):pass 1 of 4⋯15found = False16for i0, num10 in enumerate(numbers[10, 25, 30, 42, 55, 60]):17    if num == target:18        print(f"Found {target} at index {i}")⋯All 4 passes — pass 1 is the card abovepassinumtargetfound
1010——
2125——
3230——
434242True
6found ← True⋯16for i, num in enumerate(numbers):17    if num42 == target42:18        print(f"Found {target42} at index {i3}")19        found→ True = True20        break21if not found:⋯outputFound 42 at index 3
7users ← [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]⋯24# Practical: search with validation25print("\n--- Practical example ---")26users→ [{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}] = [27    {"id": 1, "name": "Alice", "active": True},28    {"id": 2, "name": "Bob", "active": False},29    {"id": 3, "name": "Charlie", "active": True},30]31search_id→ 99 = 99⋯output
--- Practical example ---
8for user in users:pass 1 of 3⋯33for user{'id': 1, 'name': 'Alice', 'active': True} in users[{'id': 1, 'name': 'Alice', 'active': True}, {'id': 2, 'name': 'Bob', 'active': False}, {'id': 3, 'name': 'Charlie', 'active': True}]:34    if user["id"] == search_id:35        print(f"Found user: {user['name']}")⋯All 3 passes — pass 1 is the card abovepassusersearch_id
1{'id': 1, 'name': 'Alice', 'active': True}—
2{'id': 2, 'name': 'Bob', 'active': False}—
3{'id': 3, 'name': 'Charlie', 'active': True}99
9else:⋯35        print(f"Found user: {user['name']}")36        break37else:38    print(f"User {search_id99} not found")⋯outputUser 99 not found

All 4 passes — pass 1 is the card above
pass	`i`	`num`	`target`
1	0	10	—
2	1	25	—
3	2	30	—
4	3	42	42

All 4 passes — pass 1 is the card above
pass	`i`	`num`	`target`	`found`
1	0	10	—	—
2	1	25	—	—
3	2	30	—	—
4	3	42	42	True

All 3 passes — pass 1 is the card above
pass	`i`	`num`	`target`
1	0	10	—
2	1	25	—
3	2	30	30

All 3 passes — pass 1 is the card above
pass	`i`	`num`	`target`	`found`
1	0	10	—	—
2	1	25	—	—
3	2	30	30	True

All 6 passes — pass 1 is the card above
pass	`i`	`num`	`target`
1	0	10	—
2	1	25	—
3	2	30	—
4	3	42	—
5	4	55	—
6	5	60	99

All 6 passes — pass 1 is the card above
pass	`i`	`num`	`found`	`target`
1	0	10	—	—
2	1	25	—	—
3	2	30	—	—
4	3	42	—	—
5	4	55	—	—
6	5	60	False	99

All 4 passes — pass 1 is the card above
pass	`i`	`num`	`target`
1	0	10	—
2	1	25	—
3	2	30	—
4	3	42	42

All 4 passes — pass 1 is the card above
pass	`i`	`num`	`target`	`found`
1	0	10	—	—
2	1	25	—	—
3	2	30	—	—
4	3	42	42	True

All 4 passes — pass 1 is the card above
pass	`i`	`num`	`target`
1	0	10	—
2	1	25	—
3	2	30	—
4	3	42	42

All 4 passes — pass 1 is the card above
pass	`i`	`num`	`target`	`found`
1	0	10	—	—
2	1	25	—	—
3	2	30	—	—
4	3	42	42	True

All 3 passes — pass 1 is the card above
pass	`user`	`search_id`
1	{'id': 1, 'name': 'Alice', 'active': True}	—
2	{'id': 2, 'name': 'Bob', 'active': False}	—
3	{'id': 3, 'name': 'Charlie', 'active': True}	99

for-else is a Pythonic way to handle "not found" scenarios.

for-else The `else` block runs only if the loop wasn't broken out of.

Exercise: refactoring.py

Explore Pythonic alternatives to break/continue