[Tutor] Re: Files and such

David Rock david at graniteweb.com
Sat Oct 2 18:29:24 CEST 2004

* Prospero <prospero at prosperosisland.co.uk> [2004-09-30 17:45]:
> Greetings!
> Still hoping someone can give me an answer on this. (Problem repeated
> below.) It seems such an obvious thing but neither the online
> information I have seen nor the one book I own on Python seem to
> address it.
> I need to save some numbers in a text file. This bit I can do no
> problem but then I need a different part of the program to read these
> numbers one set at a time, starting at the beginning and stopping at
> the end. For preference the file should be plain text so that I can
> amend it by hand if necessary. Any clues about how to do this would be
> much appreciated.
> The numbers are in groups of six, all single- or double-digit
> integers. The file would be added to one group at a time. The image I
> have in mind is of each group occupying one line, separated either by
> commas or spaces, but this does not matter as long as the format is
> clear enough to allow human editing.

If you are looking to store them as comma separated lists and you are
using Python 2.3, then the csv module is your friend:

Here is a simple csv reader example:

And here is the reader example in action using ipython (I highly
recommend ipython for interactive shell work ;-)

Contents of sample.csv:

$ ipython
Python 2.3.3 (#1, Jul  6 2004, 06:02:39)
Type "copyright", "credits" or "license" for more information.

IPython 0.6.0 -- An enhanced Interactive Python.
?       -> Introduction to IPython's features.
@magic  -> Information about IPython's 'magic' @ functions.
help    -> Python's own help system.
object? -> Details about 'object'. ?object also works, ?? prints more.

In [1]: import csv

In [2]: reader = csv.reader(file("sample.csv"))

In [3]: for row in reader:
   ...:    print row
['1', '2', '3', '4', '5', '6']
['3', '5', '7', '46', '77', '88']
['2', '6', '13', '7', '23', '5']

As you can see, the csv module will easily create a list by parsing a
comma-separated line of data. I use this a LOT in text processing

David Rock
david at graniteweb.com
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