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Use a Python for loop to process each value from an iterable, such as a list or string. Use a while loop to repeat work as long as a condition is true. range() supplies integer sequences; break exits a loop, continue skips to its next iteration, and a loop’s else runs when it finishes without a break.
How a Python for loop works
A for loop takes values one at a time from an iterable, in the order that iterable provides them. An iterable can be a list, a string, or another object that supplies items; the loop is not inherently a numeric counter.
names = ["Ada", "Linus", "Grace"]
for name in names:
print(name)Here, names is the source of values. The indented statements form the loop body, which runs once for each name.
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Using range() for integer progressions
range() is useful when a loop needs a sequence of integers. Its stop value is excluded, so range(2, 8, 2) produces 2, 4, and 6—not 8.
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for number in range(2, 8, 2):
print(number) # 2, 4, 6range(stop) starts at zero. You can also specify a start and a step, including a negative step to count downward. If you need a sequence’s index, range(len(sequence)) can provide one; when the index is not needed, iterating over the values directly is usually clearer.
When to choose for versus while
| Loop | How it gets its next iteration | Typical stopping rule |
|---|---|---|
for |
Gets successive values from an iterable. | Stops when the iterable is exhausted, unless control flow exits it earlier. |
while |
Checks a Boolean condition. | Stops when the condition becomes false, unless control flow exits it earlier. |
Choose for for a task such as “do this for each item.” Choose while for “keep doing this until a condition changes.” A while condition is checked before each iteration, so if it is false at the start, the body runs zero times.
How a while loop stops
A while loop repeats while its condition is true. The loop body should update state or otherwise make the condition able to become false; otherwise, the loop can continue indefinitely.
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while attempts < 3:
print("Try", attempts + 1)
attempts += 1The condition allows three iterations. Each pass increases attempts; after it reaches 3, the condition is false and the loop ends.
How break and continue change a loop
breakexits the nearest enclosing loop immediately, even if the iterable has more values.continueskips the rest of the current iteration and proceeds to the next iteration of that loop.
for item in items:
if should_skip(item):
continue
if is_match(item):
print(item)
breakIn this example, skipped items do not reach the match check. Once a matching item is printed, break ends the loop. In nested loops, both statements affect only the nearest enclosing loop—the innermost one—not every loop around it.
What a loop’s else clause means
A loop’s else clause runs if the loop finishes normally without executing break. With a for loop, that means the iterable was exhausted; with a while loop, it means the condition became false. The else does not run if the loop ends through break, return, or an exception.
for item in items:
if item == target:
print("Found")
break
else:
print("Not found")Indent the else at the same level as for: it belongs to the loop, not the inner if. This pattern reports a failed search only after the loop has checked all items without finding the target.
Editing a collection during iteration
Adding or removing elements from the same collection a loop is traversing can produce confusing results, because the collection changes while the loop is using it. The Python tutorial advises iterating over a copy or building a new collection instead. For example, iterate over a shallow copy when changes to the original are needed during traversal:
for item in items.copy():
if should_remove(item):
items.remove(item)For transformations or filtering, creating a separate result collection is another way to avoid changing the sequence being traversed.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Official Python documentation
The Python Software Foundation’s Python 3.14.8 tutorial on control flow explains iteration, range(), loop control, and loop else. The Python 3.14.8 language reference for compound statements specifies the statement semantics. Documentation version noted here: Python 3.14.8.
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