For Loop Syntax#

We have seen how while loops repeat as long as a condition holds. A very common pattern is iterating over every item in a sequence — every character in a string, every number in a range, every element in a list. Python’s for loop is designed exactly for this.

If you heard “For each student in the class, record a grade,” you would naturally process one student at a time, in order, until the list is exhausted. Python’s syntax captures that idea directly:

for item in iterable:
    statement(s)

On each pass through the loop, item is bound to the next value from iterable. When the iterable is exhausted the loop ends.

Iterating Over a String#

A string is a sequence of characters, so we can loop over it one character at a time. Run it and try a different string:

>>> def one_char_per_line(s: str) -> None:
...     for ch in s:
...         print(ch)
...
>>> one_char_per_line("hi!")
h
i
!

Compare this with the equivalent while loop that requires an explicit index:

>>> s = "hi!"
>>> i = 0
>>> while i < len(s):
...     print(s[i])
...     i += 1
...
h
i
!

The for version keeps the emphasis on the characters, not the secondary bookkeeping. There is no index to initialise, no i += 1 to remember, and no risk of an infinite loop.

Iterating Over a List#

The same syntax works for any sequence, including lists. Run it and change the scores:

>>> scores = [88, 73, 95, 61]
>>> total = 0
>>> for score in scores:
...     total += score
...
>>> print("Total:", total)
Total: 317

Iterating Over a Range#

To repeat something a fixed number of times, or to produce a sequence of integers, combine for with range(). Run it live:

>>> for i in range(5):
...     print(i)
...
0
1
2
3
4

range(5) generates the integers 0, 1, 2, 3, 4. The full details of range() are covered in The range() Function.

When to Use `for` vs. `while`#

Use a for loop when:

You are iterating over a known sequence (string, list, range).
The number of iterations is determined up front.

Use a while loop when:

The number of iterations depends on something that changes during the loop (user input, a computed condition).
You need the while True / break sentinel pattern.

Break and Continue#

break exits the innermost loop immediately; continue skips the rest of the current iteration and moves to the next. Both work inside for loops just as they do inside while loops. Run it and try other words:

>>> def find_first_vowel(s: str) -> str | None:
...     for ch in s.lower():
...         if ch in "aeiou":
...             return ch
...     return None
...
>>> print(find_first_vowel("Python"))
o

Here return exits the function as soon as the first vowel is found; a break would exit only the loop and continue in the function body.

For Loop Syntax

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