On 14/01/2014 19:56, Ethan Furman wrote:
Duh.  Here's the text, as well.  ;)

%s, because it is the most general, has the most convoluted resolution:

   - input type is bytes?
     pass it straight through

   - input type is numeric?
     use its __xxx__ [1] [2] method and ascii-encode it (strictly)

   - input type is something else?
     use its __bytes__ method; if there isn't one, raise an exception [3]

Examples:

     >>> b'%s' % b'abc'
     b'abc'

     >>> b'%s' % 3.14
     b'3.14'

     >>> b'%s' % 'hello world!'
     Traceback (most recent call last):
     ...
     TypeError: 'hello world' has no __bytes__ method, perhaps you need
to encode it?


For completeness I believe %r and %a should be included here as well. FTR %a appears to have been introduced in 3.2, but I couldn't find anything in the What's New and there's no note in the docs http://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting to indicate when it first came into play.

--
My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language.

Mark Lawrence

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