[Python-Dev] Use for enumerate()

Tim Peters tim.one@comcast.net
Sun, 28 Apr 2002 00:36:52 -0400

>>>>> Challenge 3: do it faster and with less code.
>>> it should work even if the file is too large
>>> to fit in memory (as long as each individual line fits in memory).

[Raymond Hettinger]
> def getline(filename, lineno):
>     if lineno < 1:
>         return ''
>     f = open(filename)
>     g = f.readline
>     return (reduce(lambda x,y: g(), range(lineno), ''), f.close())[0]

This is shorter than Guido's, but you don't imagine it's faster, right?
Calling a Python-level function for each line read is more expensive than a
few measly trips around the eval loop for each line read, even if the latter
has to build a two-tuple each time.  Guido's comes in at about 4.8 seconds
on my test, and this version at about 5.5.  I believe my first stab is still
the quickest correct version we've seen, at about 2.9.