Python For loop

A for loop lets you iterate over a sequence of values. In Python, the sequence can be a list, tuple, string, range, dictionary, or any iterable.

Basic idea

In a for loop you specify a loop variable and an iterable to step through:

for item in iterable:
    # use item inside the loop

Example 1 — Tuple of colours

Here the loop variable color takes each value from a tuple:

for color in ('red', 'orange', 'yellow', 'green', 'cyan', 'blue', 'violet'):
    print(color)

Example 2 — Numbering items with enumerate

Instead of manually updating a counter, use enumerate to get the index (starting at 1) and the value:

colors = ('red', 'orange', 'yellow', 'green', 'cyan', 'blue', 'violet')
for i, color in enumerate(colors, start=1):
print(f"{i}-th color of the rainbow is {color}")

Example 3 — Different types in one iterable

The items in a sequence can be of mixed types:

for item in (1, 2, 3, 'one', 'two', 'three'):
    print(item)

Example 4 — Looping over a range

range(start, stop, step) generates a sequence of integers:

for n in range(1, 6):  # 1, 2, 3, 4, 5
    print(n)

Example 5 — Strings are iterable

Iterating over a string yields its characters:

for ch in "Python":
    print(ch)

Example 6 — Dictionaries

Use .items() to get key–value pairs:

capitals = {"UK": "London", "France": "Paris", "Japan": "Tokyo"}
for country, city in capitals.items():
print(f"{city} is the capital of {country}")

Example 7 — break, continue, and for…else

break exits the loop early; continue skips to the next iteration. The optional else block runs only if the loop wasn’t terminated by break.

numbers = [2, 4, 6, 9, 12]
for x in numbers:
if x % 2 != 0:
print("Found an odd number:", x)
break
else:
print("All numbers were even")  # runs only if no break happened

Example 8 — List comprehension (compact looping)

A concise way to build lists from a loop:

squares_of_evens = [n*n for n in range(1, 11) if n % 2 == 0]
print(squares_of_evens)  # [4, 16, 36, 64, 100]

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Key takeaways: use for to iterate over any iterable; prefer enumerate for counters; use range for integer sequences; and remember control tools like break, continue, and for…else.