[Python-Dev] PEP 461 - Adding % and {} formatting to bytes

Ethan Furman ethan at stoneleaf.us
Thu Jan 16 08:51:38 CET 2014

On 01/15/2014 06:45 AM, Brett Cannon wrote:
> This is why I have argued that if you specify it as "if there is a format spec specified, then the return value from
> calling __format__() will have str.decode('ascii', 'strict') called on it" you get the support for the various
> number-specific format specs for free.

It may work like this under the hood, but it's an implementation detail.  Since the numeric format codes will call int, 
index, or float on the object (to handle subclasses), we could then call __format__ on the resulting int or float to do 
the heavy lifting; but since __format__ on anything else would never be called I don't want to give that impression.

> It also means if you pass in a string that you just want the strict ASCII bytes
> of then you can get it with {:s}.

This isn't going to happen.  If the user wants a string to be in the byte stream, it has to either be a bytes literal or 
explicitly encoded [1].


[1] Apologies if this has already been answered.  I wanted to make sure I responded to all the ideas/objects, and I may 
have responded more than once to some.  It's been a long few threads.  ;)

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