Cycle an iterable forever in Python

Define a generator that repeatedly yields items from an iterable, cycling back to the beginning infinitely.

Easy Python 3.9+ Aug 9, 2026 Comprehensions & generators 14 views 0 copies

generators cycle iteration infinite-loop

Python code

14 lines

Python 3.9+

def cycle_generator(iterable):
    """Yield items from iterable forever, cycling back to the start."""
    items = list(iterable)  # Convert to list so it can restart
    index = 0
    while True:
        yield items[index]
        index = (index + 1) % len(items)


if __name__ == "__main__":
    colors = ["red", "green", "blue"]
    gen = cycle_generator(colors)
    for _ in range(8):
        print(next(gen), end=" ")

Output

stdout

red green blue red green blue red green

How it works

The key is converting the input iterable into a list with list(iterable) so we can restart from index 0 after reaching the end. An infinite while True loop drives the generator, and the modulo operator (index + 1) % len(items) wraps the index back to zero. Because the generator never raises StopIteration, you must control consumption externally, usually with next() or itertools.islice.

Common mistakes

Using the original iterable directly (e.g., a generator object) which can't be replayed after exhaustion
Forgetting modulo when len(items) is zero, causing a ZeroDivisionError
Infinite loops in user code when no break or limit is applied

Variations

Replace the whole function with `itertools.cycle(iterable)` from the standard library
Use a `for` loop with `enumerate` and `next` to take a fixed number of items

Real-world use cases

Round-robin task scheduling: cycle through worker IDs to assign jobs evenly.
Rotating color palettes for charts or UI themes where colors repeat predictably.
Infinite background animation payloads that alternate frames without ever ending.

Cycle an iterable forever in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

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How it works

Common mistakes

Variations

Real-world use cases

More from Comprehensions & generators

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