Non-lazy evaluation version of map in Python3?

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)

You can set up a zero length deque to do this:

with open("output.csv", "w") as f:
    writer = csv.writer(f)
    collections.deque(map(writer.writerow, data),0)

This is the same way that itertools.consume(iterator, None) recipe works. It functionally will exhaust the iterator without building the list.

You can also just use the consume recipe from itertools.

But a loop is more readable and Pythonic to me, but YMMV.

If you don't care about the return value, then map is not the best tool for the job. A simple for would be better:

for d in data:
    writer.writerow(d)

That'll work fine in Python 2.x and 3.x. Notice that map is useful when you want to create a new list, if you're traversing over an iterable just for the effect, then use a for.