Python Control Flow — if/elif/else, for while Loops, break/continue/pass

Control flow decides what code runs and how many times. In this lesson, you’ll learn conditions (if/elif/else), loops (for, while), and loop controls (break, continue, pass) with clear examples.

1) Conditions: if, elif, else

Use conditions to run code only when a test is True.

age = 17
if age >= 18:
    print("You can vote.")
elif age >= 16:
    print("You can apply for a learner's driving permit.")
else:
    print("Focus on school and fun!")
  

How Python treats values in conditions

In if statements, some values are treated as False: 0, 0.0, empty strings "", empty containers like [], {}, set(), and None. Most other values are treated as True. This makes simple checks easy.

items = []
if items:            # empty list is treated as False
    print("Has items")
else:
    print("No items")

Combining Conditions

temp = 28
is_raining = False
if temp > 25 and not is_raining:
    print("Go for a walk!")
  

Inline Conditional (Ternary)

A compact way to write if/else in one line:

age = 18
label = "adult" if age >= 18 else "minor"
print(label)  # adult

Equivalent expanded form:

if age >= 18:
    label = "adult"
else:
    label = "minor"

2) for Loops

for loops iterate over a sequence (list, string, range, etc.).

# Iterate over a list
fruits = ["apple", "banana", "mango"]
for f in fruits:
    print(f)
# Iterate with index
for i, f in enumerate(fruits, start=1):
    print(i, f)
# Iterate a fixed number of times
for n in range(3):
    print("Hello", n)   # 0, 1, 2
  

Note: range is exclusive of the stop value. You can also specify a step:

# start, stop, step (ascending)
for n in range(0, 6, 2):
    print(n)   # 0, 2, 4

# start, stop, step (descending)
for n in range(10, 0, -2):
    print(n)   # 10, 8, 6, 4, 2

for ... else (loop-else)

The else runs only if the loop did not break.

# Find the first even number; otherwise print "none found"
nums = [3, 5, 7]
for n in nums:
    if n % 2 == 0:
        print("First even:", n)
        break
else:
    print("No even numbers")
  

3) while Loops

Run while a condition remains True. Be careful to avoid infinite loops.

count = 3
while count > 0:
    print("Countdown:", count)
    count -= 1
print("Blast off!")
  

A Common Pattern: Input Validation

tries = 0
password = "python123"
while tries < 3:
    guess = input("Enter password: ")
    if guess == password:
        print("Welcome!")
        break
    tries += 1
else:
    print("Too many attempts.")
  

4) Loop Controls: break, continue, pass

break — stop the loop now

for n in range(1, 10):
    if n == 5:
        break
    print(n)
# prints 1..4 then stops
  

continue — skip this iteration

for n in range(1, 6):
    if n % 2 == 0:
        continue   # skip even numbers
    print(n)
# prints 1, 3, 5
  

pass — do nothing (placeholder)

for task in ["todo1", "todo2"]:
    # TODO: implement later
    pass
  

5) Practical Mini-Examples

a) Sum of numbers 1..100

total = 0
for n in range(1, 101):
    total += n
print(total)
  

b) FizzBuzz (classic)

for n in range(1, 21):
    if n % 15 == 0:
        print("FizzBuzz")
    elif n % 3 == 0:
        print("Fizz")
    elif n % 5 == 0:
        print("Buzz")
    else:
        print(n)
  

c) Search with loop-else

names = ["Ali", "Ammar", "Sara"]
target = "Zain"
for name in names:
    if name == target:
        print("Found:", name)
        break
else:
    print("Not found")
  

Common Pitfalls & Tips

• Indentation matters: every block under if, for, while must align.
• Don’t modify a list while iterating it: iterate over a copy or build a new list.
• Prefer enumerate() over range(len(...)) — clearer and safer.
• Use break early to exit when done: avoids extra work.
• Leverage for ... else: perfect for “search or report not found”.

Key Takeaways

• if / elif / else choose which block runs based on conditions.
• Inline conditional (x if cond else y) is a compact way to write simple decisions.
• for iterates sequences; while repeats while a condition is true.
• break exits a loop, continue skips this iteration, pass is a placeholder.
• for/while ... else runs the else only if the loop didn’t break.
• Short-circuit logic: use and as a guard (avoid errors) and or for defaults (with care).
• Prefer enumerate() over range(len(...)); don’t modify a list while iterating it.

What’s next? In the next lesson, we’ll learn how to bundle logic into reusable pieces with Functions — definitions, arguments (positional, default, *args, **kwargs), return values, scope, lambdas, and recursion.