[Tutor] Writing/reading lists to a file

[Liam Clarke]

Hi Hans,

If you're looking to store lists as lists, may I recommend the cPickle module?
It's good for most times when you want to store an object as an object.

>>> import cPickle
>>> a = [1,2,3]
>>> b = [4,5,6]
>>> c = [7,8,9]
>>> d = [a,b,c]
>>> d
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> print d[0][1]
2
>>> f = file("filetosaveto","wb")
>>> cPickle.dump(d, f)
>>> f.close()
>>> del d
>>> f = file("filetosaveto","rb")
>>> newD = cPickle.load(f)
>>> f.close()
>>> newD
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> newD[0][1]
2

Regards,

Liam Clarke

On 12/28/05, Hans Dushanthakumar <Hans.Dushanthakumar at navman.com> wrote:
>
> Hi,
>    Is there any easy way of writing lists to a file and more
> importantly, reading it back as a list of lists rather than as a list of
> strings.
>
> Eg:
>
> >>> t = ["t1", "PASS", 31]
> >>> f = open("pass.txt","a+")
> >>> f.write(str(t) + "\n")
> >>> f.write(str(t) + "\n")
> >>> f.close()
>
> At this stage, the file contains two lines.
>
> Now, if I use the readlines() function to read it back, heres what I
> get:
> >>> f = open("pass.txt","r+")
> >>> r = f.readlines()
> >>> r
> ["['t1', 'PASS', 31]\n", "['t1', 'PASS', 31]\n", "['t1', 'PASS', 31]\n"]
> >>> r[0]
> "['t1', 'PASS', 31]\n"
>
> So, r[0] is now a string. Is there ant direct way of extracting the list
> from this string?
>
> Or alternatively, can I read the file as a list of lists rather than
> list of strings (which is what readlines() appears to do).
>
> Thanks,
> Hans
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