I would like to suggest reopening this issue, but with an alternative approach: provide some functions in the tqdm namespace (e.g. a tqdm.itertools subpackage) that behave like itertools, but provide the length if available, so that one can do (e.g.)

from tqdm import tqdm, itertools  # tqdm.itertools, not the stdlib itertools

for ... in tqdm(itertools.product(...)): ....

where tqdm.itertools.product is defined essentially as

class product:
    def __init__(self, *args):
        self._it = itertools.product(*args)  # the stdlib one
        try:
            self._len = len(args[0]) * len(args[1]) * ...
        except TypeError:  # (raised by one of the len() calls)
            self._len = None

    def __iter__(self):
        # Return the stdlib C iterator so there's no overhead when iterating,
        # only when initializing.
        return self._it

    def __len__(self):
        if self._len is not None:
            return self._len
        else:
            # Whatever makes tqdm.tqdm understand that the length is not available.
            raise TypeError(...)

Thoughts?

Uh oh!

tqdm versions of generators #225

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