[Python-Dev] PEP 460: allowing %d and %f and mojibake

Victor Stinner victor.stinner at gmail.com
Sat Jan 11 18:41:49 CET 2014


I'm in favor of adding support of formatting integer and floatting
point numbers in the PEP 460: %d, %u, %o, %x, %f with padding and
precision (%10d, %010d, %1.5f) and sign (%-i, %+i) but without
alternate format ("{:#x}"). %s would also accept int and float for

int and float subclasses would not be handled differently, their
__str__ and __format__ would be ignored.

Other int-like and float-like types (ex: defining __int__ or
__index__) are not supported. Explicit cast would be required.

For %s, the choice between string and number is made using
"(PyLong_Check() || PyFloat_Check())".

If you agree, I will modify the PEP. If Antoine disagree, I will fork
the PEP 460 ;-)


%s should not support precision (ex: %.100s), use Unicode for that.


The PEP 460 should not reintroduce bytes+unicode, implicit decoding or
implement encoding.

b'x=%s' % 10 is well defined, it's pure bytes. If you consider that
bytes should not contain text, why does the bytes type have methods
like isalpha() or upper()? And why binary files have a readline()
method? A "line" doesn't mean anything in pure bytes.

It's an example of "practicality beats purity". Python 3 should not
enforce Unicode if the developers *chose* to use bytes to handle mixed
binary/text protocols like HTTP.

But I'm against of adding "%r" and "%a" because they use Unicode and
would require an implicit encoding. type(ascii(obj)) is str, not
bytes. If you really want to use repr() and ascii(), encode the result


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