Hi all,
I am running Python 2.5 on Feisty Ubuntu. I came across some code that
is substantially slower when in a method than in a function.
################# START SOURCE #############
# The function
def readgenome(filehandle):
s = ''
for line in filehandle.xreadlines():
if '>' in line:
continue
s += line.strip()
return s
# The method in a class
class bar:
def readgenome(self, filehandle):
self.s = ''
for line in filehandle.xreadlines():
if '>' in line:
continue
self.s += line.strip()
################# END SOURCE ##############
When running the function and the method on a 20,000 line text file, I
get the following:
>>> cProfile.run("bar.readgenome(open('cb_foo'))")
20004 function calls in 10.214 CPU seconds
Ordered by: standard name
ncalls tottime percall cumtime percall
filename:lineno(function)
1 0.000 0.000 10.214 10.214 <string>:1(<module>)
1 10.205 10.205 10.214 10.214 reader.py:11(readgenome)
1 0.000 0.000 0.000 0.000 {method 'disable' of
'_lsprof.Profiler' objects}
19999 0.009 0.000 0.009 0.000 {method 'strip' of 'str'
objects}
1 0.000 0.000 0.000 0.000 {method 'xreadlines' of
'file' objects}
1 0.000 0.000 0.000 0.000 {open}
>>> cProfile.run("z=r.readgenome(open('cb_foo'))")
20004 function calls in 0.041 CPU seconds
Ordered by: standard name
ncalls tottime percall cumtime percall
filename:lineno(function)
1 0.000 0.000 0.041 0.041 <string>:1(<module>)
1 0.035 0.035 0.041 0.041 reader.py:2(readgenome)
1 0.000 0.000 0.000 0.000 {method 'disable' of
'_lsprof.Profiler' objects}
19999 0.007 0.000 0.007 0.000 {method 'strip' of 'str'
objects}
1 0.000 0.000 0.000 0.000 {method 'xreadlines' of
'file' objects}
1 0.000 0.000 0.000 0.000 {open}
The method takes > 10 seconds, the function call 0.041 seconds!
Yes, I know that I wrote the underlying code rather inefficiently, and
I can streamline it with a single file.read() call instead if an
xreadlines() + strip loop. Still, the differences in performance are
rather staggering! Any comments?
Thanks,
Iddo
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