python - Non-lazy evaluation version of map in Python3?

Question

I'm trying to use map in Python3. Here's some code I'm using:

import csv

data = [
    [1],
    [2],
    [3]
]

with open("output.csv", "w") as f:
    writer = csv.writer(f)
    map(writer.writerow, data)

However, since map in Python3 returns an iterator, this code doesn't work in Python3 (but works fine in Python2 since that version of map always return a list)

My current solution is to add a list function call over the iterator to force the evaluation. But it seems odd (I don't care about the return value, why should I convert the iterator into a list?)

Any better solutions?

Answer 1

Using map for its side-effects (eg function call) when you're not interested in returned values is undesirable even in Python2.x. If the function returns None, but repeats a million times - you'd be building a list of a million Nones just to discard it. The correct way is to either use a for-loop and call:

for row in data:
    writer.writerow(row)

or as the csv module allows, use:

writer.writerows(data)

If for some reason you really, really wanted to use map, then you can use the consume recipe from itertools and generate a zero length deque, eg:

from collections import deque
deque(map(writer.writerow, data), maxlen=0)