zip() function does not work as expected

zip() function does not work as expected - Printable Version

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zip() function does not work as expected - AyCaramba - Jan-31-2018

This is my code for creating 2 lists, zipping them together, unzipping them and printout the unzipped lists.

list1 = [1, 2, 3]  # create 2 lists: list1, list2
list2 = ['A', 'B', 'C']
zipped = zip(list1, list2)  # create zip object from the 2 lists: zipped
test1, test2 = zip(*zipped)  # unzip the zip: test1, test2
print(list(test1))
print(list(test2))

As expected, I get the output:

Output:[1, 2, 3]
['A', 'B', 'C']

Now, I want to print the values of zipped, using list(zipped) after defining my zip object. After line 3, I insert the additional print command.

list1 = [1, 2, 3]  # create 2 lists
list2 = ['A', 'B', 'C']
zipped = zip(list1, list2)  # create zip object from the 2 lists: zipped
print(list(zipped))
test1, test2 = zip(*zipped)  # unzip the zip using *
print(list(test1))
print(list(test2))

I get an error massage:

Error:line 5, in <module>
    test1, test2 = zip(*zipped)  # unzip the zip using *
ValueError: not enough values to unpack (expected 2, got 0)

Why do I get an error? Does the list(zipped) command in line 4 somehow destroy my zip object?
When I recreate zipped in line 5, after printing its value out, everything works fine again.

list1 = [1, 2, 3]  # create 2 lists
list2 = ['A', 'B', 'C']
zipped = zip(list1, list2)  # create zip object from the 2 lists: zipped
print(list(zipped)) 
zipped = zip(list1, list2)  # recreate zip object from the 2 lists: zipped
test1, test2 = zip(*zipped)  # unzip the zip using *
print(list(test1))
print(list(test2))

That's now the output I expected in the second code.

Output:[(1, 'A'), (2, 'B'), (3, 'C')]
[1, 2, 3]
['A', 'B', 'C']

I dont understand why I need to recreate my zip object to get the output I expected.

RE: zip() function does not work as expected - Gribouillis - Jan-31-2018

(Jan-31-2018, 04:47 PM)AyCaramba Wrote: Does the list(zipped) command in line 4 somehow destroy my zip object?

The zip object is an iterable. The expression list(zipped) consumes the iterable. There are no more items in zipped after this expression.