For Loop Syntax

Note

Source: Adapted from the C# edition (foreach/foreachintro.rst and for/forstatements.rst). Python’s for loop is a foreach — it unifies C#’s separate foreach and for constructs into one statement. No type declaration is needed for the loop variable. The break and continue statements work the same way as in C#.

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:

def one_char_per_line(s):
    for ch in s:
        print(ch)

one_char_per_line("hi!")

Output:

h
i
!

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

i = 0
while i < len(s):
    print(s[i])
    i += 1

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:

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

Output:

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():

for i in range(5):
    print(i)

Output:

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.

def find_first_vowel(s):
    for ch in s.lower():
        if ch in "aeiou":
            return ch
    return None

print(find_first_vowel("Python"))

Output:

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.