当你不知道你的对象是否可以迭代时如何迭代

Question

Sometimes I have multiple axes in axes[0] , and sometimes just one. So to iterate over it/them, I use the following:

for ax,_x in [(axes[0], X[0])] if len(X)==1 else zip(axes[0],X):

What is the idiomatic way to do this?

Answer 1

In general, the best way is to just iterate. Don't ask for permission (with if checks, rather wrap it in a try-except block for handling the "forgiveness" cases.

As others have commented though, you shouldn't create different cases if X is a list of size 1 , that still is iterable. If you use zip it will stop at the shortest iterable:

>>> l = [1, 2, 3]    
>>> y = [1, 2]

>>> list(zip(l, y))
[(1, 1), (2, 2)]

If you need to work with all values of the longer iterable and provide defaults for the missing values of the shorted one, use zip_longest from itertools with an appropriate fillvalue :

>>> from itertools import zip_longest

>>> list(zip_longest(l, y, fillvalue=0))
[(1, 1), (2, 2), (3, 0)]