[issue21547] '!s' formatting documentation bug
New submission from Joshua Landau: In the docs for 2.x about the formatting syntax: https://docs.python.org/2/library/string.html#format-string-syntax it says "Two conversion flags are currently supported: '!s' which calls str() on the value, and '!r' which calls repr()." but for unicode formatters, '!s' calls unicode() instead. See http://stackoverflow.com/questions/23773816/why-python-str-format-doesnt-cal... for the question that found this. ---------- assignee: docs@python components: Documentation messages: 218863 nosy: Joshua.Landau, docs@python priority: normal severity: normal status: open title: '!s' formatting documentation bug versions: Python 2.7 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue21547> _______________________________________
Eric V. Smith added the comment: I suggest using whatever language explains what "u'%s' %obj" does. It's the same behavior.
From the SO question, given:
class A(object): def __str__(self): return 'as str' def __unicode__(self): return u'as unicode' Then:
'%s' % A() 'as str' u'%s' % A() u'as unicode'
and:
'{!s}'.format(A()) 'as str' u'{!s}'.format(A()) u'as unicode'
---------- nosy: +eric.smith _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue21547> _______________________________________
Steven Barker added the comment: The behavior of !s with the format() methods isn't exactly the same as %s with % formatting. With the latter, the conversion depends on the type of the result string, which in turn depends on whether the format string *or any of the values values* is unicode: >>> class X(): def __str__(self): return "str" def __unicode__(self): return u"unicode" >>> "%s %s" % ("foo", X()) 'foo str' >>> "%s %s" % (u"foo", X()) u'foo unicode' >>> u"%s %s" % ("foo", X()) u'foo unicode' >>> u"%s %s" % (u"foo", X()) u'foo unicode' The format methods are more consistent, always returning the same type as the format string regardless of the types of the arguments (and using the appropriate converter): >>> "{} {!s}".format("foo", X()) 'foo str' >>> "{} {!s}".format(u"foo", X()) 'foo str' >>> u"{} {!s}".format("foo", X()) u'foo unicode' >>> u"{} {!s}".format(u"foo", X()) u'foo unicode' The documentation for %s conversion (in the second table here: https://docs.python.org/2/library/stdtypes.html#string-formatting-operations ) also suggests that it always uses str(), though the footnote for that table entry alludes to the behavior shown above without ever mentioning using unicode() for conversions explicitly. ---------- nosy: +Steven.Barker _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue21547> _______________________________________
Changes by Ezio Melotti <ezio.melotti@gmail.com>: ---------- nosy: +ezio.melotti type: -> behavior _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue21547> _______________________________________
Serhiy Storchaka <storchaka+cpython@gmail.com> added the comment: Python 2.7 is no longer supported. ---------- nosy: +serhiy.storchaka resolution: -> out of date stage: -> resolved status: open -> closed _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue21547> _______________________________________
participants (5)
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Eric V. Smith -
Ezio Melotti
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Joshua Landau
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Serhiy Storchaka
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Steven Barker