Hi All,
The following function was showing up in my profiles as a large bottle neck:
# Slow version
def RMSBand(self, histogram):
"""Calculates the root-mean-squared value for the given colour stream
histogram."""
intermediateResult = map(lambda (i, h): h*(i**2), zip(histogram,
range(255)))
totalSum = sum(intermediateResult)
# calculate rms
return math.sqrt(totalSum / self.Area())
So after a bit of trial and error I came up with the following function which
is a lot faster:
# Fast version
def RMSBand(self, histogram):
"""Calculates the root-mean-squared value for the given colour stream
histogram."""
totalSum = 0
for i, h in enumerate(histogram):
totalSum += h*(i**2)
# calculate rms
return math.sqrt(totalSum / self.Area())
My question is why is the second method so much faster?
Is it the removal of the extra function calls?
Is it skipping the creation of a list?
Do the basic arithmetic operators get pushed up into C code?
Any insights into the whats really happening behind the scenes would be
appreciated.
Keir
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