[Python] Editing a file by substitution

[GammaPoint]

Hi, what I'd like to do is edit an input file for a calculation with Python. Let's say that I have an input file like the following



BLAH BLAH BLAH

Other inputs, Volume 940 m^3, maybe some more stuff

STUFF STUFF


So let's say I want to edit this file and change Volume from 940 to 950.

This is how I would guess I would do something like it:



import re
expr=r'.*Volume\s+(?P<VolValue>\d+[.]?[\d+]?)'
exprComp=re.compile(expr)
infile=open('myfile','r')
outfile=open('outfile','w')

for line in infile:
match=exprComp.search(line)
if match:
newline=<HELP ME!>
print >> outfile, newline
else:
print >> outfile, line
infile.close()
outfile.close()


So what I would like to do in the section labeled <HELP ME!> is to use something like the re.sub() function and replace the contents of the "VolValue" group with another number. However I am not sure how exactly to do this. Help please pythonistas :)

[days_of_ruin]

Does the input file have to be like that?It would be much
better if you used an xml file for data like that and used
ElementTree module http://www.learningpython.com/2008/05/07/elegant-xml-parsing-using-the-elementtree-module/.A whole lot simpler.

[GammaPoint]

Does the input file have to be like that?It would be much
better if you used an xml file for data like that and used
ElementTree module http://www.learningpython.com/2008/05/07/elegant-xml-parsing-using-the-elementtree-module/.A whole lot simpler.

Yeah, the input file is read by a different program that I'm not associated with. So it needs to be like that. That XML module you linked to is nice looking though- I might need that sort of thing with something I'll be doing in the next couple months.

[days_of_ruin]

Here ya go!:guitar:


import re
expr=r'.*Volume\s+(?P<VolValue>\d+[.]?[\d+]?)'
exprComp=re.compile(expr)
infile=open('myfile','r')
outfile=open('outfile','r+')

for line in infile:
match=exprComp.search(line)
if match:
mynumber ="950"
t = re.compile(match.group(1))

s = t.sub(mynumber,line)
print >> outfile, s
else:
print >> outfile,line
infile.close()
outfile.close()

[ghostdog74]

no need re, simple string methods will do.


for line in open("file"):
n=line.strip().split()
if "Volume" in line:
n[n.index("Volume")+1]="950"
print " ".join(n)
else:
print line.strip()