I just tried to run this script with Python 3.3. Unfortunately it's about twice as slow than with Python 2.7.
#!/usr/bin/env python
from sys import stdin
def main():
for line in stdin:
try:
fields = line.split('"', 6)
print(fields[5])
except:
pass
if __name__ == '__main__':
main()
Here are the results:
$ time zcat access.log.gz | python3 -m cProfile ./ua.py > /dev/null
real 0m13.276s
user 0m18.977s
sys 0m0.484s
$ time zcat access.log.gz | python2 -m cProfile ./ua.py > /dev/null
real 0m6.139s
user 0m11.693s
sys 0m0.408s
Profiling shows that the additional time is spend in print:
$ zcat access.log.gz | python3 -m cProfile ./ua.py | tail -15
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.000 0.000 0.000 0.000 <frozen importlib._bootstrap>:1594(_handle_fromlist)
196806 0.234 0.000 0.545 0.000 codecs.py:298(decode)
1 0.000 0.000 13.598 13.598 ua.py:3(<module>)
1 4.838 4.838 13.598 13.598 ua.py:6(main)
1 0.000 0.000 13.598 13.598 {built-in method exec}
1 0.000 0.000 0.000 0.000 {built-in method hasattr}
4300456 4.726 0.000 4.726 0.000 {built-in method print}
196806 0.312 0.000 0.312 0.000 {built-in method utf_8_decode}
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
4300456 3.489 0.000 3.489 0.000 {method 'split' of 'str' objects}
$ zcat access.log.gz | python2 -m cProfile ./ua.py | tail -10
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.000 0.000 6.573 6.573 ua.py:3(<module>)
1 3.894 3.894 6.573 6.573 ua.py:6(main)
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
4300456 2.680 0.000 2.680 0.000 {method 'split' of 'str' objects}
How can I avoid this overhead? Has it something to do with UTF-8?
Python 3 decodes data read from stdin
and encodes again to stdout
; it is not so much the print()
function that is slower here as the unicode-to-bytes conversion and vice-versa.
In your case you probably want to bypass this and deal with bytes only; you can access the underlying BufferedIOBase
implementation through the .buffer
attribute :
from sys import stdin, stdout
try:
bytes_stdin, bytes_stdout = stdin.buffer, stdout.buffer
except AttributeError:
bytes_stdin, bytes_stdout = stdin, stdout
def main():
for line in bytes_stdin:
try:
fields = line.split(b'"', 6)
bytes_stdout.write(fields[5] + b'\n')
except IndexError:
pass
if __name__ == '__main__':
main()
You'll now have to use stdout.write()
as print()
insists on writing to the stdout
TextIOBase
implementation.
Note that the .split()
now uses a bytes literal b'"'
and we write a bytes-literal b'\\n'
as well (which normally would be taken care of by print()
).
The above is compatible with Python 2.6 and up. Python 2.5 doesn't support the b
prefix.
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