Question

In coding competitions we encounter inputs like:

2 3

4 5

So we do the following:

m, n = [int(x) for x in raw_input().split(' ')]

Is there a faster way of doing the same thing?

Answer 1

For all practical purposes, That’s about as fast as you can get. On some machines, you may see a speedup on the order or a couple percent if you go with map instead of a list comprehension, but that’s not guaranteed.

Here’s some quick timings on my machine:

from itertools import imap
#map
>>> timeit.timeit('x,y = map(int,line.split(" "))','from __main__ import line')
4.7857139110565186
>>> timeit.timeit('x,y = map(int,line.split())','from __main__ import line')
4.5680718421936035
#list comprehension
>>> timeit.timeit('x,y = [int(x) for x in line.split(" ")]','from __main__ import line')
4.3816750049591064
>>> timeit.timeit('x,y = [int(x) for x in line.split()]','from __main__ import line')
4.3246541023254395
#itertools.imap
>>> timeit.timeit('x,y = imap(int,line.split(" "))','from __main__ import line,imap')
4.431504011154175
>>> timeit.timeit('x,y = imap(int,line.split())','from __main__ import line,imap')
4.3257410526275635
#generator expression
>>> timeit.timeit('x,y = (int(x) for x in line.split(" "))','from __main__ import line')
4.897794961929321
>>> timeit.timeit('x,y = (int(x) for x in line.split())','from __main__ import line')
4.732620000839233

Surprisingly, split() seems to perform better than split(" ").

---

If you’re guaranteed to have ascii input of numbers between 0 and 9, you can do a good bit better using ord:

>>>timeit.timeit('x,y = [ord(x)-48 for x in line.split(" ")]','from __main__ import line')
1.377655029296875
>>> timeit.timeit('x,y = [ord(x)-48 for x in line.split()]','from __main__ import line')
1.3243558406829834

But that imposes a severe restriction on your inputs.

---

One other idea that you could try (I have no idea what the performance implications would be), but you could read your lines from sys.stdin:

import sys
for line in sys.stdin:
    x,y = [ord(x)-48 for x in line.split()]