I bet someone in the world has written code like: foo = str(**dynamic-args())
And therefore, disabling "silly" combinations of arguments will break their code occasionally. On Sun, Dec 15, 2019, 9:09 AM Serhiy Storchaka <storch...@gmail.com> wrote: > Currently str() takes up to 3 arguments. All are optional and > positional-or-keyword. All combinations are valid: > > str() > str(object=object) > str(object=buffer, encoding=encoding) > str(object=buffer, errors=errors) > str(object=buffer, encoding=encoding, errors=errors) > str(encoding=encoding) > str(errors=errors) > str(encoding=encoding, errors=errors) > > The last three are especially surprising. If you do not specify an > object, str() ignores values of encoding and errors and returns an empty > string. > > bytes() and bytearray() are more limited. Valid combinations are: > > bytes() > bytes(source=object) > bytes(source=string, encoding=encoding) > bytes(source=string, encoding=encoding, errors=errors) > > I propose several changes: > > 1. Forbids calling str() without object if encoding or errors are > specified. It is very unlikely that this can break a real code, so I > propose to make it an error without a deprecation period. > > 2. Make the first parameter of str(), bytes() and bytearray() > positional-only. Originally this feature was an implementation artifact: > before 3.6 parameters of a C implemented function should be either all > positional-only (if used PyArg_ParseTuple), or all keyword (if used > PyArg_ParseTupleAndKeywords). So str(), bytes() and bytearray() accepted > the first parameter by keyword. We already made similar changes for > int(), float(), etc: int(x=42) no longer works. > > Unlikely str(object=object) is used in a real code, so we can skip a > deprecation period for this change too. > > 3. Make encoding required if errors is specified in str(). This will > reduce the number of possible combinations, makes str() more similar to > bytes() and bytearray() and simplify the mental model: if encoding is > specified, then we decode, and the first argument must be a bytes-like > object, otherwise we convert an object to a string using __str__. > _______________________________________________ > Python-Dev mailing list -- python-dev@python.org > To unsubscribe send an email to python-dev-le...@python.org > https://mail.python.org/mailman3/lists/python-dev.python.org/ > Message archived at > https://mail.python.org/archives/list/python-dev@python.org/message/YMIGWRUERUG66CKRJXDXNPCIDHRQJY6V/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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