importing izip from itertools module gives NameErr

问题:

I am trying to import the izip module like so:

from itertools import izip

However after recently changing over from Python 2.7 to 3 - it doesn't seem to work.

I am trying to write to a csv file:

writer.writerows(izip(variable1,2))

But I have no luck. Still encounter an error.

回答1:

In Python 3 the built-in zip does the same job as itertools.izip in 2.X(returns an iterator instead of a list). The zip implementation is almost completely copy-pasted from the old izip, just with a few names changed and pickle support added.

Here is a benchmark between zip in Python 2 and 3 and izip in Python 2:

Python 2.7:

from timeit import timeit

print(timeit('list(izip(xrange(100), xrange(100)))',
             'from itertools import izip',
             number=500000))

print(timeit('zip(xrange(100), xrange(100))', number=500000))

Output:

1.9288790226
1.2828938961

Python 3:

from timeit import timeit

print(timeit('list(zip(range(100), range(100)))', number=500000))

Output:

1.7653984297066927

In this case since zip's arguments must support iteration you can not use 2 as its argument. So if you want to write 2 variable as a CSV row you can put them in a tuple or list:

writer.writerows((variable1,2))

Also from itertools you can import zip_longest as a more flexible function which you can use it on iterators with different size.

回答2:

One of the ways which helped me is:

try:
    from itertools import izip as zip
except ImportError: # will be 3.x series
    pass

回答3:

Use zip instead of izip directly in python 3, no need to import anything.

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