Replace Pattern

[Sorin Marti]

Hello all,

I am quite new to python and want to do the following:

- open a file (done)
- read each line (done)
- search a pattern in the file and replace it
- write the new file

I want to replace the date. example:
INSERT INTO organization VALUES ('Brussels','Br abant','23 10 1954');

should be:
INSERT INTO organization VALUES ('Brussels','Br abant','1954-10-24');

What i've done:

import os,sys
try:
fi = open('test.sql' , 'r')
while fi.readline():
line = fi.readline();

except IOError:
print 'Can\'t open file for reading.'
sys.exit(0)

Thanks for any help.

[Peter Otten]

Re: Replace Pattern

Sorin Marti wrote:
[color=blue]
> Hello all,
>
> I am quite new to python and want to do the following:
>
> - open a file (done)
> - read each line (done)
> - search a pattern in the file and replace it
> - write the new file
>
> I want to replace the date. example:
> INSERT INTO organization VALUES ('Brussels','Br abant','23 10 1954');
>
> should be:
> INSERT INTO organization VALUES ('Brussels','Br abant','1954-10-24');
>[/color]

I'm assuming the 24 is a typo, and that you want to change the date format
from 'DD MM YYYY' to 'YYYY-MM-DD'. Otherwise use

line.replace("2 3 10 1954", "1954-10-24")

There must be simpler ways, but this is what I did:

import re

r = re.compile(r"\' (\d\d) (\d\d) (\d\d\d\d)'")

def adjustDate(m):
return "'%s-%s-%s'" % (m.group(3), m.group(2), m.group(1))

infile = file("in.sql")
outfile = file("out.sql", "w")
for line in infile:
outfile.write(r .sub(adjustDate , line))

The type of search pattern used is called regular expression, and if you
want to understand them, A. M. Kuchling has written a nice Howto for Python
users.
[color=blue]
> What i've done:
>
> import os,sys
> try:
> fi = open('test.sql' , 'r')
> while fi.readline():
> line = fi.readline();
>
> except IOError:
> print 'Can\'t open file for reading.'[/color]

That's the most probable error, but you cannot be sure. In those rare cases
when a problem occurs in the while loop, you are misleading the user -
which could well be yourself :-)
While it's good to start with proper error handling as early as possible, in
the case of a small conversion script, a traceback printed by an uncaught
exception could even be more helpful.
[color=blue]
> sys.exit(0)[/color]

Why would you want to exit your script with 0 (indicating success) if and
error occured?


Peter

[Christopher Koppler]

Re: Replace Pattern

mas@semafor.ch (Sorin Marti) wrote in message news:<6f878011. 0402082345.69d7 4d13@posting.go ogle.com>...[color=blue]
> Hello all,
>
> I am quite new to python and want to do the following:
>
> - open a file (done)
> - read each line (done)
> - search a pattern in the file and replace it
> - write the new file
>
> I want to replace the date. example:
> INSERT INTO organization VALUES ('Brussels','Br abant','23 10 1954');
>
> should be:
> INSERT INTO organization VALUES ('Brussels','Br abant','1954-10-24');
>
> What i've done:
>
> import os,sys
> try:
> fi = open('test.sql' , 'r')
> while fi.readline():
> line = fi.readline();
>
> except IOError:
> print 'Can\'t open file for reading.'
> sys.exit(0)
>
> Thanks for any help.[/color]

how 'bout this:

import re

pattern = r"(\d\d) (\d\d) (\d\d\d\d)"
replacement = r"\3-\2-\1"

try:
infile = file('test.sql' , 'r')
outfile = file('new.sql', 'w')
except IOError:
print "Can't open file."
else:
for line in infile:
modified = re.sub(pattern, replacement, line)
outfile.write(m odified)
infile.close()
outfile.close()


--
Christopher