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[Python-Dev] PEP 461 Final?

Glenn Linderman v+python at g.nevcal.com
Fri Jan 17 20:40:37 CET 2014 
On 1/17/2014 8:49 AM, Ethan Furman wrote:
> %s is restricted in what it will accept::
>
>   - input type supports Py_buffer?
>     use it to collect the necessary bytes
>
>   - input type is something else?
>     use its __bytes__ method; if there isn't one, raise a TypeError
>
> Examples:
>
>     >>> b'%s' % b'abc'
>     b'abc'
>
>     >>> b'%s' % 3.14
>     Traceback (most recent call last):
>     ...
>     TypeError: 3.14 has no __bytes__ method
>
>     >>> b'%s' % 'hello world!'
>     Traceback (most recent call last):
>     ...
>     TypeError: 'hello world' has no __bytes__ method, perhaps you need 
> to encode it?

If you produce a helpful error message for str (re: encoding), might it 
not be appropriate to produce a helpful error message for builtin number 
types (, perhaps you need a numeric format code?)?
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