Question

I’ve been playing around with the map function in Python and I was looking for some help in understanding the following behaviour:

foo="12345"
print map(int,foo)

gives you [1, 2, 3, 4, 5]. Obviously int(foo) spits out 12345. So what exactly is happening? Since strings are iterable by character, would the above two lines be synonymous with

print [int(x) for x in foo]

I know they will output the same result but is there anything different going on behind the scenes? Is one more efficient or better than another? Is one more “pythonic”?

Thanks a lot!

Answer 1

map() may be somewhat faster than using list comprehension in some cases and in some cases map is slower than list comprehensions.

when using a built-in function:

python -mtimeit -s'xs=xrange(1000)' 'map(int,"1234567890")'
10000 loops, best of 3: 18.3 usec per loop

python -mtimeit -s'xs=xrange(1000)' '[int(x) for x in "1234567890"]'
100000 loops, best of 3: 20 usec per loop

with lambda,map() becomes slow:

python -mtimeit -s'xs=xrange(1000)' '[x*10 for x in "1234567890"]'
100000 loops, best of 3: 6.11 usec per loop

python -mtimeit -s'xs=xrange(1000)' 'map(lambda x:x*10,"1234567890")'
100000 loops, best of 3: 11.2 usec per loop

But, in python 3x map() returns a map object, i.e. an iterator