pythonloopsgenerator

How can I infinitely loop an iterator in Python, via a generator or other?


It's my understanding that using a Generator is the best way to achieve something like this, but I'm open to suggestions.

Specifically, one use case is this: I'd like to print some items alongside another list, of an arbitrary length, truncating the initial iterator as necessary.

Here is working python code that demonstrates the exact example behavior I desire:

    def loop_list(iterable):
        """
        Return a Generator that will infinitely repeat the given iterable.

        >>> l = loop_list(['sam', 'max'])
        >>> for i in range(1, 11):
        ...     print i, l.next()
        ... 
        1 sam
        2 max
        3 sam
        4 max
        5 sam
        6 max
        7 sam
        8 max
        9 sam
        10 max

        >>> l = loop_list(['sam', 'max'])
        >>> for i in range(1, 2):
        ...     print i, l.next()
        ... 
        1 sam
        """
        iterable = tuple(iterable)
        l = len(iterable)
        num = 0
        while num < l:
            yield iterable[num]
            num += 1
            if num >= l:
                num = 0

The Problem / My Question

As you may have noticed, this only works on lists/tuples/iterables that implement __getitem__ (if I'm not mistaken). Ideally, I'd like to be able to pass any iterable, and receive a generator that can properly loop over it's content.

If there's a better way to do something like this without a generator, I'm fine with that as well.


Solution

  • You can use itertools.cycle (source included on linked page).

    import itertools
    
    a = [1, 2, 3]
    
    for element in itertools.cycle(a):
        print element
    
    # -> 1 2 3 1 2 3 1 2 3 1 2 3 ...