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From: Stephen Hansen <me+python@ixokai.io>
Newsgroups: comp.lang.python
Subject: Re: Most probably a stupid question, but I still want to ask
Date: Sun, 10 Apr 2016 22:42:23 -0700
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On Sun, Apr 10, 2016, at 10:18 PM, Rustom Mody wrote:
> On Monday, April 11, 2016 at 10:17:13 AM UTC+5:30, Stephen Hansen wrote:
> > On Sun, Apr 10, 2016, at 09:03 PM, Fillmore wrote:
> > > and the (almost always to be avoided) use of eval()
> > 
> > FWIW, there's ast.literal_eval which is safe and there's no reason to
> > avoid it.
> 
> Its error reporting is clunky:
> 
> >>> from ast import literal_eval as le
> >>> le("(1)")
> 1
> >>> le("(1,)")
> (1,)
> >>> le("1")
> 1
> >>> le("{1:x}")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "/usr/lib/python2.7/ast.py", line 80, in literal_eval
>     return _convert(node_or_string)
>   File "/usr/lib/python2.7/ast.py", line 63, in _convert
>     in zip(node.keys, node.values))
>   File "/usr/lib/python2.7/ast.py", line 62, in <genexpr>
>     return dict((_convert(k), _convert(v)) for k, v
>   File "/usr/lib/python2.7/ast.py", line 79, in _convert
>     raise ValueError('malformed string')
> ValueError: malformed string

So? Worst case scenario, someone puts invalid data into the file and it
throws an exception. Could it be more specific? Maybe, but I don't see
why it needs to be. If your input isn't reliably formatted, catch
ValueError and log it and fix (either what wrote it or change how you
read it).

--S