Python zip behavour – Can someone explain this

Edit: the answer previously stated ‘generator’ instead of ‘iterator’, but @juanpa.arrivillaga correctly pointed out that the zip object is in fact an iterator (which works essentially the same from a user perspective, but does not have the same overhead)

z is an iterator and your first use of it in print(list(z)) exhausts it. You should repeat z=zip(x,y) before the 4th print statement. Note that you still see it as a <zip object> in the 3rd print statement because it is, it’s just an exhausted zip object. And the first use doesn’t exhaust it.

x = [1]
y = [2]
z = zip(x,y)    # zip object created, ready to yield values

print(z)        # print z, the object
print(list(z))  # exhaust z into a list, print the list
print(z)        # print z, the object (now exhausted)
print(list(z))  # try to exhaust z into a list again, nothing there, print []

Try this:

x=[1]
y=[2]
z=zip(x,y)

print(z)
print(list(z))
print(z)
z=zip(x,y)
print(list(z))
print(list(zip(x,y)))