seek in a file

[Emile van Sebille]

"Andreas Penzel" <mail at andreas-penzel.de> wrote in message
news:a7s4q4$no0i9$1 at ID-69142.news.dfncis.de...
> "Steven Majewski" wrote:
>
> > Are the files too big to fit in memory ?
>
> the file is about 1 MB, i have to test out working
>
> > What do you want to do with the lines ?
> > ( I hope you weren't planning on trying to modify a line in a file:
> >   because of the variable length on lines, if you don't write
> >   exactly the same number of chars back, you will either overwite
> >   the next line, or leave an extra partial line after your edited
> >   line. Most text editors read the whole file into memory and then
> >   write out a new file after it's modified in memory. )
>
> In the file are barcodes of products, one per line.
> The program has to look if the scanned code from the barcode-scanner
is
> identically with one in the file included. This is important because
the
> barcode-scanner sometimes works not correct. All i need is an
search-routine
> that compares the scanned code with the codes in the file. If there is
an
> code, the programs waits for the next code.
>

Then you probably want to read the whole file in and restructure for
optimal access.  The duplicate values for multiple keys is no longer an
issue.  Build a look up dictionary and use it:

#--untested--
productlist = open('\path\and\filename').readlines()
upcdict = {}
for rec in productlist:
    product, upccode = rec.split(delimiter)
    upcdict[upccode] = product  # or None if you're just validating

try: upcdict[scannedcode]
except: invalid code handling


HTH,

--

Emile van Sebille
emile at fenx.com

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