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Bytes, strings, and unicode? #30
Description
I see this warning in the standard library:
/tmp/pygrate2/Lib/codecs.py:506: Py3xWarning: The first string is 'str' while the second is 'unicode': mixed bytes, str and unicode operands cannot be used in string concatenation in Python 3.x: convert the operand(s) so that they are the same type.
self.charbuffer += newchars
Since Python3 doesn't have the unicode type per se, I'm wondering if this warning is quite right? As I understand the situation (and my memory is a bit fuzzy...):
- Python2 has the types
strandunicodebut not a typebytes. Thebytes()function returnsstrs. - Python3 has the types
bytesandstrbut notunicode.
If I've got that (roughly) correct, I wonder whether the warning at the top of this issue is correct and/or as accurate as it could be? I think that str + unicode in Python2 will always map to str + str in Python3? Or are there certain types of strings/unicode strings in Python2 that will map to bytes in Python3?
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nanjekyejoannah commentedon May 22, 2023
Yes, you are correct, the
uprefix just exists for backward compatibility, i.e, no-op per se, its not supported in semantics to say unicode = str, that is to say no Python 3 code uses theuprefix or is expected to. Any code still using theuprefix is most likely assuming the genuine existence of the unicode type as was the case in Python 2. I think in short supportinguin python 3 is not a feature, just exists for convenience. If we look at it as a supported solely for compatibility, the warning is correct, if we assume it is a feature the warning needs fixing.ltratt commentedon May 22, 2023
I'm not sure this is entirely about
u"blah"strings, but I might be wrong. The warning we're giving is really saying the+operator won't work as expected in Python3. In one sense, I suppose that's true, but I think it's not very useful, because Python3 won't have let a user construct aunicodestring by definition.Now that I think about it, I'm not even sure if the user can do much about this warning? Can they convert their string type(s) in a way that will make their code forward compatible?
nanjekyejoannah commentedon May 22, 2023
By making the strings involved in the
+operation of the same type. str + str or bytes + bytes , if we tookuto be a feature u'str' + 'str' shouldnt lead to a warning.