String join() method used with for loop

Question

I need your help, because I don\'t understand why is possible to use the join() method with a forloop as an argument.

Ex:

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Answer 1

The statement (str(x) for x in list) is called a generator expression:

>>> (str(x) for x in [1,2,3])
 at 0x7fc916f01d20>

What this does is create an object that can be iterated over exactly once, and yields elements that would be created one at a time. You can iterate over it as you would a list, like this:

>>> gen = (str(x) for x in [1,2,3])
>>> for s in gen:
...     print s
... 
1
2
3

A generator expression is iterable, so what the join function does is iterate over it and join its values.