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pythoniterable-unpacking

Zipping an empty iterable

I want to loop through an iterable of tuples and store each value in a new variable. I can do this with zip: x, y = zip(*enumerate(range(0,30,5)))

But this doesn't work if the iterable is empty

x, y = zip(*enumerate(range(0,-1,5)))
Traceback (most recent call last):
  File "C:\Python36\lib\site-packages\IPython\core\interactiveshell.py", line 3267, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-35-76960294a673>", line 1, in <module>
    x, y = zip(*enumerate(range(0,-1,5)))
ValueError: not enough values to unpack (expected 2, got 0)

Because zip returns an empty iterable instead of an iterable containing two empty lists

How can I handle the case where the iterable is empty?

Solution

  • Awkward special casing:

    x, y = [*zip(*your_iterable)] or [(), ()]

    or just not using zip(*...). Your zip(*enumerate(...)) can be replaced by constructing the indices with range:

    y = tuple(range(0,-1,5))
x = tuple(range(len(y)))

    I'm calling tuple here to replicate the behavior of zip, but depending on what you're doing, that may not be necessary.