Here is my Perl and Python script to do some simple text processing from about 21 log files, each about 300 KB to 1 MB (maximum) x 5 times repeated (total of 125 files, due to the log repeated 5 times).
Python Code (code modified to use compiled re and using re.I)
#!/usr/bin/python
import re
import fileinput
exists_re = re.compile(r'^(.*?) INFO.*Such a record already exists', re.I)
location_re = re.compile(r'^AwbLocation (.*?) insert into', re.I)
for line in fileinput.input():
fn = fileinput.filename()
currline = line.rstrip()
mprev = exists_re.search(currline)
if(mprev):
xlogtime = mprev.group(1)
mcurr = location_re.search(currline)
if(mcurr):
print fn, xlogtime, mcurr.group(1)
Perl Code
#!/usr/bin/perl
while (<>) {
chomp;
if (m/^(.*?) INFO.*Such a record already exists/i) {
$xlogtime = $1;
}
if (m/^AwbLocation (.*?) insert into/i) {
print "$ARGV $xlogtime $1\n";
}
}
And, on my PC both code generates exactly the same result file of 10,790 lines. And, here is the timing done on Cygwin's Perl and Python implementations.
User@UserHP /cygdrive/d/tmp/Clipboard
# time /tmp/scripts/python/afs/process_file.py *log* *log* *log* *log* *log* >
summarypy.log
real 0m8.185s
user 0m8.018s
sys 0m0.092s
User@UserHP /cygdrive/d/tmp/Clipboard
# time /tmp/scripts/python/afs/process_file.pl *log* *log* *log* *log* *log* >
summarypl.log
real 0m1.481s
user 0m1.294s
sys 0m0.124s
Originally, it took 10.2 seconds using Python and only 1.9 secs using Perl for this simple text processing.
(UPDATE) but, after the compiled re version of Python, it now takes 8.2 seconds in Python and 1.5 seconds in Perl. Still Perl is much faster.
Is there a way to improve the speed of Python at all OR it is obvious that Perl will be the speedy one for simple text processing.
By the way this was not the only test I did for simple text processing... And, each different way I make the source code, always always Perl wins by a large margin. And, not once did Python performed better for simple m/regex/ match and print stuff.
Please do not suggest to use C, C++, Assembly, other flavours of Python, etc.
I am looking for a solution using Standard Python with its built-in modules compared against Standard Perl (not even using the modules). Boy, I wish to use Python for all my tasks due to its readability, but to give up speed, I don't think so.
So, please suggest how can the code be improved to have comparable results with Perl.
UPDATE: 2012-10-18
As other users suggested, Perl has its place and Python has its.
So, for this question, one can safely conclude that for simple regex match on each line for hundreds or thousands of text files and writing the results to a file (or printing to screen), Perl will always, always WIN in performance for this job. It as simple as that.
Please note that when I say Perl wins in performance... only standard Perl and Python is compared... not resorting to some obscure modules (obscure for a normal user like me) and also not calling C, C++, assembly libraries from Python or Perl. We don't have time to learn all these extra steps and installation for a simple text matching job.
So, Perl rocks for text processing and regex.
Python has its place to rock in other places.
Update 2013-05-29: An excellent article that does similar comparison is here. Perl again wins for simple text matching... And for more details, read the article.
This is exactly the sort of stuff that Perl was designed to do, so it doesn't surprise me that it's faster.
One easy optimization in your Python code would be to precompile those regexes, so they aren't getting recompiled each time.
exists_re = re.compile(r'^(.*?) INFO.*Such a record already exists')
location_re = re.compile(r'^AwbLocation (.*?) insert into')
And then in your loop:
mprev = exists_re.search(currline)
and
mcurr = location_re.search(currline)
That by itself won't magically bring your Python script in line with your Perl script, but repeatedly calling re in a loop without compiling first is bad practice in Python.
Hypothesis: Perl spends less time backtracking in lines that don't match due to optimisations it has that Python doesn't.
What do you get by replacing
^(.*?) INFO.*Such a record already exists
with
^((?:(?! INFO).)*?) INFO.*Such a record already
or
^(?>(.*?) INFO).*Such a record already exists
Function calls are a bit expensive in terms of time in Python. And yet you have a loop invariant function call to get the file name inside the loop:
fn = fileinput.filename()
Move this line above the for loop and you should see some improvement to your Python timing. Probably not enough to beat out Perl though.
In general, all artificial benchmarks are evil. However, everything else being equal (algorithmic approach), you can make improvements on a relative basis. However, it should be noted that I don't use Perl, so I can't argue in its favor. That being said, with Python you can try using Pyrex or Cython to improve performance. Or, if you are adventurous, you can try converting the Python code into C++ via ShedSkin (which works for most of the core language, and some - but not all, of the core modules).
Nevertheless, you can follow some of the tips posted here:
I expect Perl be faster. Just being curious, can you try the following?
#!/usr/bin/python
import re
import glob
import sys
import os
exists_re = re.compile(r'^(.*?) INFO.*Such a record already exists', re.I)
location_re = re.compile(r'^AwbLocation (.*?) insert into', re.I)
for mask in sys.argv[1:]:
for fname in glob.glob(mask):
if os.path.isfile(fname):
f = open(fname)
for line in f:
mex = exists_re.search(line)
if mex:
xlogtime = mex.group(1)
mloc = location_re.search(line)
if mloc:
print fname, xlogtime, mloc.group(1)
f.close()
Update as reaction to "it is too complex".
Of course it looks more complex than the Perl version. The Perl was built around the regular expressions. This way, you can hardly find interpreted language that is faster in regular expressions. The Perl syntax...
while (<>) {
...
}
... also hides a lot of things that have to be done somehow in a more general language. On the other hand, it is quite easy to make the Python code more readable if you move the unreadable part out:
#!/usr/bin/python
import re
import glob
import sys
import os
def input_files():
'''The generator loops through the files defined by masks from cmd.'''
for mask in sys.argv[1:]:
for fname in glob.glob(mask):
if os.path.isfile(fname):
yield fname
exists_re = re.compile(r'^(.*?) INFO.*Such a record already exists', re.I)
location_re = re.compile(r'^AwbLocation (.*?) insert into', re.I)
for fname in input_files():
with open(fname) as f: # Now the f.close() is done automatically
for line in f:
mex = exists_re.search(line)
if mex:
xlogtime = mex.group(1)
mloc = location_re.search(line)
if mloc:
print fname, xlogtime, mloc.group(1)
Here the def input_files() could be placed elsewhere (say in another module), or it can be reused. It is possible to mimic even the Perl's while (<>) {...} easily, even though not the same way syntactically:
#!/usr/bin/python
import re
import glob
import sys
import os
def input_lines():
'''The generator loops through the lines of the files defined by masks from cmd.'''
for mask in sys.argv[1:]:
for fname in glob.glob(mask):
if os.path.isfile(fname):
with open(fname) as f: # now the f.close() is done automatically
for line in f:
yield fname, line
exists_re = re.compile(r'^(.*?) INFO.*Such a record already exists', re.I)
location_re = re.compile(r'^AwbLocation (.*?) insert into', re.I)
for fname, line in input_lines():
mex = exists_re.search(line)
if mex:
xlogtime = mex.group(1)
mloc = location_re.search(line)
if mloc:
print fname, xlogtime, mloc.group(1)
Then the last for may look as easy (in principle) as the Perl's while (<>) {...}. Such readability enhancements are more difficult in Perl.
Anyway, it will not make the Python program faster. Perl will be faster again here. Perl is a file/text cruncher. But--in my opinion--Python is a better programming language for more general purposes.
来源：https://stackoverflow.com/questions/12793562/text-processing-python-vs-perl-performance