[Python-Dev] PEP 461 - Adding % and {} formatting to bytes (original) (raw)

Brett Cannon brett at python.org
Thu Jan 16 15:45:14 CET 2014

On Thu, Jan 16, 2014 at 2:51 AM, Ethan Furman <ethan at stoneleaf.us> wrote:

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.

I'm arguing it's not an implementation detail but a definition of how bytes.format() would work.

Since the numeric format codes will call int, index, or float on the object (to handle subclasses),

But that's only because the numeric types choose to as part of their format() implementation; it is not inherent to str.format().

we could then call format on the resulting int or float to do the heavy lifting;

It's not just the heavy lifting; it does all the lifting for format specifications.

but since format on anything else would never be called I don't want to give that impression.

Fine, if you're worried about bytes.format() overstepping by implicitly calling str.encode() on the return value of format() then you will need bytes__format() to get equivalent support.

-Brett

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]. -- Ethan [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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