String from File -> List without parsing

[Gregor Horvath]

Hi,

given the dynamic nature of python I assume that there is an elegant
solution for my problem, but I did not manage to find it.

I have a file that contains for example on line:

['147', '148', '146']

when I read the file

f = file("I050901.i ds").readlines( )

I have a string

f[0] == "['147', '148', '146']"

How can I turn this string into a list

li == ['147', '148', '146']

without parsing?

--
Greg

[Jean-François Doyon]

Re: String from File -> List without parsing

Gregor,

You want to use eval():

Python 2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit (Intel)] on
win32
Type "help", "copyright" , "credits" or "license" for more information.[color=blue][color=green][color=darkred]
>>> eval('[3,54,5]')[/color][/color][/color]
[3, 54, 5][color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Cheers,
J.F.

Gregor Horvath wrote:[color=blue]
> Hi,
>
> given the dynamic nature of python I assume that there is an elegant
> solution for my problem, but I did not manage to find it.
>
> I have a file that contains for example on line:
>
> ['147', '148', '146']
>
> when I read the file
>
> f = file("I050901.i ds").readlines( )
>
> I have a string
>
> f[0] == "['147', '148', '146']"
>
> How can I turn this string into a list
>
> li == ['147', '148', '146']
>
> without parsing?
>
> --
> Greg[/color]

[John Machin]

Re: String from File -> List without parsing

Gregor Horvath wrote:[color=blue]
> Hi,
>
> given the dynamic nature of python I assume that there is an elegant
> solution for my problem, but I did not manage to find it.
>
> I have a file that contains for example on line:
> ['147', '148', '146']
> when I read the file
> f = file("I050901.i ds").readlines( )[/color]

Y3K bug alert :-)
[color=blue]
> I have a string
> f[0] == "['147', '148', '146']"[/color]

The last (or sole) line is highly likely to be "['147', '148',
'146']\n". If there are multiple lines in the file, all but the last
will definitely have "\n" at the end.
[color=blue]
> How can I turn this string into a list
> li == ['147', '148', '146']
> without parsing?[/color]

Something like this:
[color=blue][color=green][color=darkred]
>>> def munch(astrg):[/color][/color][/color]
.... return [x[1:-1] for x in astrg.rstrip("\ n")[1:-1].split(", ")]
....[color=blue][color=green][color=darkred]
>>> munch("['147', '148', '146']")[/color][/color][/color]
['147', '148', '146'][color=blue][color=green][color=darkred]
>>> munch("['147', '148', '146']\n")[/color][/color][/color]
['147', '148', '146'][color=blue][color=green][color=darkred]
>>> munch("['147']\n")[/color][/color][/color]
['147'][color=blue][color=green][color=darkred]
>>> # Warning: various flavours of "nothing" give the same result:
>>> munch("['']\n")[/color][/color][/color]
[''][color=blue][color=green][color=darkred]
>>> munch("[]\n")[/color][/color][/color]
[''][color=blue][color=green][color=darkred]
>>> munch("\n")[/color][/color][/color]
[''][color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

This assumes that the contents are no more complicated than in your example.

Some notes:

(1) You neither want nor need to use eval.

(2) What is creating files like that? If it is a Python script, consider
writing them using the csv module; that way, other software can read
them easily.

HTH,
John

[Gregor Horvath]

Re: String from File -> List without parsing

John Machin wrote:
[color=blue][color=green]
>> f = file("I050901.i ds").readlines( )[/color]
>
> Y3K bug alert :-)[/color]

but then there is Python 3000 and Hurd, which solves all problems of
this universe :-)
[color=blue]
> Something like this:
>[color=green][color=darkred]
> >>> def munch(astrg):[/color][/color]
> ... return [x[1:-1] for x in astrg.rstrip("\ n")[1:-1].split(", ")][/color]

Thanks!
[color=blue]
> (1) You neither want nor need to use eval.[/color]

I wanted to avoid parsing, but when parsing is an 1 liner, I think its
the better solution.
[color=blue]
>
> (2) What is creating files like that? If it is a Python script, consider
> writing them using the csv module; that way, other software can read
> them easily.
>[/color]

Its a Python script.
But the file is not intended to be used by another sotware, although it
should be readable by humans. I think the python syntax is better human
readable than csv.

After all the sense of this file is to make a list persistant quickly
and easily and human readable. Maybe pickleing is a third option?

--
Gregor