It’s often necessary to iterate over multiple lists simultaneously. Suppose we’re keeping score of a game and we have two lists, one for names and one for scores:
>>> names = ["Bob", "Alice", "Eve"]
>>> scores = [42, 97, 68]
The zip function takes any number of iterable arguments and steps through
all of them at the same time until the end of the shortest iterable has been reached:
>>> for name, score in zip(names, scores):
>>> print(f"{name} had a score of {score}.")
...
Bob had a score of 42.
Alice had a score of 97.
Eve had a score of 68.
What will the above loop print after removing the last element from scores?
>>> scores.pop(-1)
68
>>> for name, score in zip(names, scores):
>>> print(f"{name} had a score of {score}.")
...
Bob had a score of 42.
Alice had a score of 97.
The loop terminates even though there are more values in names. Here, Eve isn’t included because scores only has two elements.
We can also use zip() to quickly and easily create a dict from two lists.
>>> names = ["Bob", "Alice", "Eve"]
>>> scores = [42, 97, 68]
>>> score_dict = dict(zip(names, scores))
>>> print(score_dict)
{'Bob': 42, 'Alice': 97, 'Eve': 68}
Note that the result of calling the zip function is actually a generator under the hood. You can only loop over the result of zipping once. If you try to loop over it again, the result will be empty.
>>> names = ["Bob", "Alice", "Eve"]
>>> scores = [42, 97, 68]
>>> zip_result = zip(names, scores)
# Works fine the first time!
>>> for name, score in zip_result:
... print(f"{name} had a score of {score}.")
...
Bob had a score of 42.
Alice had a score of 97.
Eve had a score of 68.
# But empty if we try to loop over it again.
>>> for name, score in zip_result:
... print(f"{name} had a score of {score}.")
...
>>>