changing some lines in a file

[Gordon McMillan]

Peter Posselt Vestergaard writes:

> Hi, I'm quite a newbie in Python-programming, so I hope you'll
> forgive me asking about some pretty things. :-) My problem is that I
> have a file in which i want to find some lines and replace them with
> some other data. I've tried a lot of things but nothing seems to
> work.

Unfortunately, you haven't said what "doesn't work" means. 

> Below is my best try, but it seems that the script stops when
> it is about to execute the line:

Stops how? With a traceback?

> line=('fi='+Form["fi"].value)
> 
> I'll be thankfull for any kind of help.
> Best regards
> 
> Peter Vestergaard
> 
> ------------------------------------------------------------------
> 
> 
> db = open("db.dat","r+")		

Why are you opening for update?
				 
> data = db.readlines()
> db.close

MIssing something?

> 
> found=0
> for line in data:
>     print found
>     if found==1:
>         if line[0:2]=='fi':
>             line=('fi='+Form["fi"].value)

Ah. Well you'll never see any results, because you're rebinding the 
variable "line" to a new string. When you return to the "for", you 
lose all your hard work.

You can either modify the data list by using 

for i in range(len(data)):
  line = data[i]
  .....
     data[i] = 'fi=' + Form[whatever]....

Or create a new list and append the modified lines to it.

(Updating a file in place usually means lots of seek()s and tells() 
and is basically never worthwhile on text files.)

>         elif line[0:2]=='la':
>             line='la='+Form["la"].value
>         elif line[0:2]=='em':
>             line='em='+Form["em"].value
>         elif line[0:2]=='ho':
>             line='ho='+Form["ho"].value
>         elif line[0:2]=='st':
>             line='st='+Form["st"].value
>             found=2
>     if line[0:9]==('id='+Form["id"].value):
>         found=1
> if found==0:
>     print '<H1>Fejl i årskortnummeret!</H1>'
>     stop 
> 
> db = open("db.dat","w")
> db.writelines(data)
> db.close
> 
> -- 
> http://www.python.org/mailman/listinfo/python-list

- Gordon