Python 3 zip list unpacking

Question

I have two lists of tuples mkp1 and mkp2 which I zip and want to unpack them later to lists. But after the first part is unpacked, the rest ist missing… Why?

Minimal example:

# list of tuples
mkp1 = [(1, 2), (3, 4), (5, 6)]
mkp2 = [(10, 20), (30, 40), (50, 60)]

# zip this list
pairs = zip(mkp1, mkp2)

# unzip this list
p1 = [kpp[0] for kpp in pairs]
p2 = [kpp[1] for kpp in pairs]
print('p1:', p1)
print('p2:', p2)

Edit: Strangely this works like I expected in Python 2.7 but not in Python 3.4.

Asked By: bastelflp

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Source

Answer 1

Ah, I found the answer: In Python 2, zip returns a list of tuples while in Python 3 it returns an iterator. This causes the second iteration to lead to an empty list.

This works:

# list of tuples
mkp1 = [(1, 2), (3, 4), (5, 6)]
mkp2 = [(10, 20), (30, 40), (50, 60)]

# zip this list
pairs = zip(mkp1, mkp2)

# unzip this list
p1, p2 = [], []
for kpp in pairs:
    p1.append(kpp[0])
    p2.append(kpp[1])

print('p1:', p1)
print('p2:', p2)

Answered By: bastelflp

Python 3 zip list unpacking

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