Control Flow

if / elif / else

age = 20
 
if age < 13:
    category = "child"
elif age < 20:
    category = "teen"
else:
    category = "adult"

Conditional (Ternary) Expression

status = "adult" if age >= 18 else "minor"

while Loops

count = 0
while count < 5:
    print(count)
    count += 1

while with else

The else block runs only if the loop completes without hitting a break.

n = 7
i = 2
while i < n:
    if n % i == 0:
        print(f"{n} is not prime")
        break
    i += 1
else:
    print(f"{n} is prime")

for Loops

Python’s for iterates over any iterable, it is not a C-style counting loop.

for fruit in ["apple", "banana", "cherry"]:
    print(fruit)
 
for i in range(5):          # 0, 1, 2, 3, 4
    print(i)
 
for i in range(2, 10, 2):   # start, stop, step -> 2, 4, 6, 8
    print(i)
 
for index, value in enumerate(["a", "b", "c"]):
    print(index, value)      # 0 a / 1 b / 2 c
 
for key, value in {"x": 1, "y": 2}.items():
    print(key, value)

enumerate over manual counters

Never write i = 0 then i += 1 inside a loop to track index. Use enumerate(iterable, start=0) instead, it is cleaner and less error prone.

break, continue, pass

for i in range(10):
    if i == 5:
        break          # exits the loop entirely
    if i % 2 == 0:
        continue        # skips to next iteration
    print(i)
 
if True:
    pass                # does nothing, a placeholder for future code

match / case (Structural Pattern Matching, Python 3.10+)

A more powerful alternative to long if/elif chains, supporting pattern destructuring.

def handle(command):
    match command.split():
        case ["go", direction]:
            print(f"Moving {direction}")
        case ["look"]:
            print("Looking around")
        case ["take", *items]:
            print(f"Taking {items}")
        case _:
            print("Unknown command")
 
handle("go north")     # Moving north
handle("take sword shield")  # Taking ['sword', 'shield']

def describe(value):
    match value:
        case 0:
            return "zero"
        case int() | float() if value < 0:
            return "negative number"
        case [x, y]:
            return f"a pair: {x}, {y}"
        case {"type": "user", "name": name}:
            return f"user named {name}"
        case _:
            return "something else"

_ is the wildcard

case _: matches anything, similar to default in other languages. It should almost always be the last case.

Nested Loops and Labeled-Break Alternative

Python has no labeled break/continue. The common workaround is a flag or refactoring into a function with return.

found = False
for i in range(5):
    for j in range(5):
        if i * j == 6:
            found = True
            break
    if found:
        break

A cleaner approach: extract the nested loops into a function and use return to exit both levels at once.

for...else and while...else

Just like while, for supports else, which runs if the loop was not exited via break. This is a genuinely underused but powerful pattern for “search and act if not found” logic.

for item in inventory:
    if item.name == "key":
        print("Found the key")
        break
else:
    print("Key not found anywhere")