[Python-Dev] local import cost

[Skip Montanaro]

Thanks to Raymond H for pointing out the probably fallacy in my original
timeit runs.  Here's a simple timer which I think gets at what I'm after:

    import time
    import math
    import sys

    N = 500000

    def fmath():
        import math

    def fpass():
        pass

    v = sys.version.split()[0]

    t = time.clock()
    for i in xrange(N):
        fmath()
    fmathcps = N/(time.clock()-t)

    t = time.clock()
    for i in xrange(N):
        fpass()
    fpasscps = N/(time.clock()-t)

    print "%s fpass/fmath: %.1f" % (v, fpasscps/fmathcps)

On my Mac I get these outputs:

    2.1.3 fpass/fmath: 5.0
    2.2.2 fpass/fmath: 5.6
    2.3b1+ fpass/fmath: 5.3

Naturally, I expect fpass() to run a lot faster than fmath().  If my
presumption is correct though, there will be a sharp increase in the ratio,
maybe in 2.0 or 2.1, or whenever nested scopes were first introduced.

I can't run anything earlier than 2.1.x (I'll see about building 2.1) on my
Mac.  I'd have to break out my Linux laptop and do a bunch of downloading
and compiling to get earlier results.