text file reformatting

iwawi iwawi123 at gmail.com
Mon Nov 1 09:58:50 CET 2010


On 1 marras, 09:59, "cbr... at cbrownsystems.com"
<cbr... at cbrownsystems.com> wrote:
> On Oct 31, 11:46 pm, iwawi <iwawi... at gmail.com> wrote:
>
>
>
>
>
> > On 31 loka, 21:48, Tim Chase <python.l... at tim.thechases.com> wrote:
>
> > > > PRJ01001 4 00100END
> > > > PRJ01002 3 00110END
>
> > > > I would like to pick only some columns to a new file and put them to a
> > > > certain places (to match previous data) - definition file (def.csv)
> > > > could be something like this:
>
> > > > VARIABLE   FIELDSTARTS     FIELD SIZE      NEW PLACE IN NEW DATA FILE
> > > > ProjID     ;       1       ;       5       ;       1
> > > > CaseID     ;       6       ;       3       ;       10
> > > > UselessV  ;        10      ;       1       ;
> > > > Zipcode    ;       12      ;       5       ;       15
>
> > > > So the new datafile should look like this:
>
> > > > PRJ01    001       00100END
> > > > PRJ01    002       00110END
>
> > > How flexible is the def.csv format?  The difficulty I see with
> > > your def.csv format is that it leaves undefined gaps (presumably
> > > to be filled in with spaces) and that you also have a blank "new
> > > place in new file" value.  If instead, you could specify the
> > > width to which you want to pad it and omit variables you don't
> > > want in the output, ordering the variables in the same order you
> > > want them in the output:
>
> > >   Variable; Start; Size; Width
> > >   ProjID; 1; 5; 10
> > >   CaseID; 6; 3; 10
> > >   Zipcode; 12; 5; 5
> > >   End; 16; 3; 3
>
> > > (note that I lazily use the same method to copy the END from the
> > > source to the destination, rather than coding specially for it)
> > > you could do something like this (untested)
>
> > >    import csv
> > >    f = file('def.csv', 'rb')
> > >    f.next() # discard the header row
> > >    r = csv.reader(f, delimiter=';')
> > >    fields = [
> > >      (varname, slice(int(start), int(start)+int(size)), width)
> > >      for varname, start, size, width
> > >      in r
> > >      ]
> > >    f.close()
> > >    out = file('out.txt', 'w')
> > >    try:
> > >      for row in file('data.txt'):
> > >        for varname, slc, width in fields:
> > >          out.write(row[slc].ljust(width))
> > >        out.write('\n')
> > >    finally:
> > >      out.close()
>
> > > Hope that's fairly easy to follow and makes sense.  There might
> > > be some fence-posting errors (particularly your use of "1" as the
> > > initial offset, while python uses "0" as the initial offset for
> > > strings)
>
> > > If you can't modify the def.csv format, then things are a bit
> > > more complex and I'd almost be tempted to write a script to try
> > > and convert your existing def.csv format into something simpler
> > > to process like what I describe.
>
> > > -tkc- Piilota siteerattu teksti -
>
> > > - Näytä siteerattu teksti -
>
> > Hi,
>
> > Thanks for your reply.
>
> > Def.csv could be modified so that every line has the same structure:
> > variable name, field start, field size and new place and would be
> > separated with semicolomns as you mentioned.
>
> > I tried your script (which seems quite logical) but I get this
>
> > Traceback (most recent call last):
> >   File "testing.py", line 16, in <module>
> >     out.write (row[slc].ljust(width))
> > TypeError: an integer is required
>
> > Yes - you said it was untested, but I can't figure out how to
> > proceed...
>
> The line
>
>     (varname, slice(int(start), int(start)+int(size)), width)
>
> should instead be
>
>     (varname, slice(int(start), int(start)+int(size)), int(width))
>
> although you give an example where there is no width - what does that
> imply? In the above case, it will throw an exception.
>
> Anyway, I think you'll find there's something a bit off in the output
> loop with the parameter passed to ljust() as well. The value given in
> your csv seems to be the absolute position, but as it's implemented by
> Tim, it acts as the relative position.
>
> Given Tim's parsing into the list fields, I have a feeling that what
> you really want instead of
>
>     for varname, slc, width in fields:
>         out.write(row[slc].ljust(width))
>     out.write('\n')
>
> is to have
>
>     s = ''
>     for varname, slc, width in fields:
>         s += " "*(width - len(s)) + row[slc]
>     out.write(s+'\n')
>
> And if that is what you want, then you will surely want to globally
> replace the name 'width' with for example 'start_column', because then
> it all makes sense :).
>
> Cheers - Chas- Piilota siteerattu teksti -
>
> - Näytä siteerattu teksti -

Yes, it's meant to be the absolute column position in a new file like
you said.

I used your changes to the csv-reading cause it seems more flexible,
but the end of the code is still not working. Here's were I stand now:

import re

parse_columns = re.compile(r'\s*;\s*')

f = file('def.csv', 'rb')
f.readline() # discard the header row
r = (parse_columns.split(line.strip()) for line in f)
fields = [
 (varname, slice(int(start), int(start)+int(size), int(width) if width
else 0))
  for varname, start, size, width in r
 ]
f.close()
print fields

out = file('out.txt', 'w')

try:
 for row in file('data.txt'):
  s = ' '
  for varname, slc, width in fields:
   s += " "*(width - len(s)) + row[slc]
  out.write(s+'\n')
finally:
 out.close()

When executed, I get this:
  File "toimi.py", line 20, in <module>
    for varname, slc, width in fields:
ValueError: need more than 2 values to unpack





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