Re: indexing in format strings

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From	Terry Reedy <tjreedy@udel.edu>
Subject	Re: indexing in format strings
Date	Fri, 11 Apr 2014 17:45:02 -0400
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On 4/11/2014 5:33 PM, blindanagram wrote:
> With:
>
>     l = [1,2,3]
>
> this:
>
>     print('{0[0]:d}..{0[2]:d}'.format(l))
>
> gives 1..3 but this:
>
>     print('{0[0]:d}..{0[-1]:d}'.format(l))
>
> gives:
>
>     Traceback (most recent call last):
>      File "<string>", line 1, in <fragment>
>     builtins.TypeError: list indices must be integers, not str
>
> which seems to me counterintuitive.
>
> I expected indexing in a format string to behave as it does elsewhere
> but this seems not to be true.

Been discussed on the tracker. Consider:

 >>> '{0[-1]}'.format({'-1': 'neg int key'})
'neg int key'

Not quoting string keys within the format string introduces ambiguity 
settled by 'string unless all digits, then int'.

-- 
Terry Jan Reedy

Thread

indexing in format strings blindanagram <noone@nowhere.net> - 2014-04-11 22:33 +0100
  Re: indexing in format strings Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-11 22:43 +0100
  Re: indexing in format strings Terry Reedy <tjreedy@udel.edu> - 2014-04-11 17:45 -0400
  Re: indexing in format strings blindanagram <noone@nowhere.net> - 2014-04-12 00:13 +0100
    Re: indexing in format strings Terry Reedy <tjreedy@udel.edu> - 2014-04-11 22:44 -0400

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