[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.python

replace string in a file

cantabile

3/15/2008 8:54:00 PM

Hi,
I've got this code :

cb = open("testfile", "r+")
f = cb.readlines()
for line in f:
rx = re.match(r'^\s*(\d+).*', line)
if not rx:
continue
else:
serial = rx.group(1)
now = time.time()
today = time.strftime('%Y%m%d00', time.localtime(now))
todayVal, serialVal = long(today), long(serial)
if todayVal <= serialVal:
todayVal = serialVal + 1
else:
todayVal += 1
line = string.replace(line, serial, "%d" %todayVal)
cb.write(line + "\n")
print 'Updated serial from "%s" to "%d"' % ( serial, todayVal )
break
cb.close()

I was expecting to replace the old value (serial) with the new one
(todayVal). Instead, this code *adds* another line below the one found...

How can I just replace it?

Thanks for your help :-)
5 Answers

AK

3/15/2008 9:25:00 PM

0

On Mar 15, 3:54 pm, Unknown <cantabile...@wanadoo.fr> wrote:
> Hi,
> I've got this code :
>
> cb = open("testfile", "r+")
> f = cb.readlines()
> for line in f:
>     rx = re.match(r'^\s*(\d+).*', line)
>     if not rx:
>         continue
>     else:
>         serial = rx.group(1)
>         now = time.time()
>         today = time.strftime('%Y%m%d00', time.localtime(now))
>         todayVal, serialVal = long(today), long(serial)
>         if todayVal <= serialVal:
>             todayVal = serialVal + 1
>         else:
>             todayVal += 1
>         line = string.replace(line, serial, "%d" %todayVal)
>         cb.write(line + "\n")
>         print 'Updated serial from "%s" to "%d"' % ( serial, todayVal )
>         break      
> cb.close()
>
> I was expecting to replace the old value (serial) with the new one
> (todayVal). Instead, this code *adds* another line below the one found...
>
> How can I just replace it?
>
> Thanks for your help :-)

What you want to do is either 1. load everything up into a string,
replace
text, close file, reopen it with 'w' flag, write string to it. OR if
file is too big, you can read each line, replace, write to a temp
file,
then when done move the file over the old one.

I think there are technical reasons why file-reading and iteration api
are not very suitable for reading and writing at the same time. I
think
you'd have to set the filepointer back one line (it can be manipulated
by giving it bytes ahead/back, so that would be difficult in itself),
then delete the line and then write new string. It may be even harder
than
that, I'm sure someone can explain this much better, but you're far
better
off with using one of the 2 methods above.. HTH, -ak

cantabile

3/15/2008 9:47:00 PM

0

Thanks, andrei. I'll try that.

Le Sat, 15 Mar 2008 14:25:21 -0700, andrei.avk a écrit :

> What you want to do is either 1. load everything up into a string,
> replace
> text, close file, reopen it with 'w' flag, write string to it. OR if
> file is too big, you can read each line, replace, write to a temp file,
> then when done move the file over the old one.

Josef Pktd

3/15/2008 11:56:00 PM

0

you can also use standard module fileinput.input with ''inplace''
option which backs up original file automatically.

from python help for fileinput:

Optional in-place filtering: if the keyword argument inplace=1 is
passed to input() or to the FileInput constructor, the file is moved
to a backup file and standard output is directed to the input file (if
a file of the same name as the backup file already exists, it will be
replaced silently).

cantabile

3/17/2008 2:04:00 AM

0

Le Sat, 15 Mar 2008 16:55:45 -0700, joep a écrit :

> you can also use standard module fileinput.input with ''inplace'' option
> which backs up original file automatically.
>
> from python help for fileinput:
>
> Optional in-place filtering: if the keyword argument inplace=1 is passed
> to input() or to the FileInput constructor, the file is moved to a
> backup file and standard output is directed to the input file (if a file
> of the same name as the backup file already exists, it will be replaced
> silently).

Thanks for the idea :)
What I do not get is how I can replace a string with that.

If I write something like:

for line in filehandle.input('myfile.txt', inplace=1):
rx = re.match(r'^\s*(\d+).*',line )
if not rx:
continue
else:
oldValue = rx.group(1)
Value = 123456789
line = string.replace(line, oldValue, "%d" Value)
print line
break

This code replaces the whole file with line, instead of replacinf the old
value with the new one. Did I forget something ?

sturlamolden

3/17/2008 2:35:00 AM

0

On 15 Mar, 21:54, Unknown <cantabile...@wanadoo.fr> wrote:

> I was expecting to replace the old value (serial) with the new one
> (todayVal). Instead, this code *adds* another line below the one found...
>
> How can I just replace it?

A file is a stream of bytes, not a list of lines. You can't just
replace a line with another, unless they have the exact same length.
You must rewrite the whole file to get it right.