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

Terry Reedy tjreedy at udel.edu
Fri Jan 17 21:56:07 CET 2014

Responding to two posts at once, as I consider them

On 1/17/2014 11:00 AM, Brett Cannon wrote:

I would rephrase it to "switch to %-formatting for bytes usage for their common code base". If they are working with actual text then using str.format() still works (and is actually nicer to use IMO). It actually might make the str/bytes relationship even clearer, especially if we start to promote that str.format() is for text and %-formatting is for bytes.

Good idea, I think: printf % formatting was invented for formatting ascii text in bytestrings as it was being output (although sprintf allowed not-output). In retrospect, I think we should have introduced unicode.format when unicode was introduced in 2.0 and perhap never have had unicode % formatting. Or we should have dropped str % instead of bytes % in 3.0.

On 1/17/2014 12:13 PM, Eric V. Smith wrote:

But if we think that %-formatting is neanderthal and will get dropped in the Python 4000 timeframe (that is, someday in the far future),

Some people, such as Martin Loewis, have a different opinion of %-formatting and will fight deprecating it ever. (I suspect that %-format opinions are influenced by one's current relation to C.)

then I think we should have some advice to give to people who are writing new 3.x code for the non-porting use-cases addressed by the PEP. I'm specifically thinking of new code that wants to format some bytes for an on-the-wire ascii-like protocol.

If we add %-formatting back in 3.5 for its original purpose, formatting ascii in bytes for output, I think we should drop the idea of later deprecating it (a few releases later) for that purpose. I think the PEP should even say so, that bytes % will remain indefinitely even if str % were to be dropped in favor of str.format.

I would consider dropping unicode(now string).mod in favor of .format to still be an eventual option, especially if someone were to write a converter.

-- Terry Jan Reedy

More information about the Python-Dev mailing list