[Python-Dev] transitioning from % to {} formatting

[Nick Coghlan]

Vinay Sajip wrote:
> You're right to be nervous: it's not hard to mangle subtypes.
> 
>>>> class mystr(str): pass
> ...
>>>> s = mystr("Abc")
>>>> s
> 'Abc'
>>>> type(s)
> <class '__main__.mystr'>
>>>> s2 = s.replace("A", "a")
>>>> s2
> 'abc'
>>>> type(s2)
> <type 'str'>

It's also difficult for the subclass to prevent this without creating an
infinite loop... (I only spent about 10 minutes looking into it the
other day, but that's what happened in all of my naive attempts at doing
it in pure Python code).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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