'True' is a keyword. (Which is now immutable in Python 3.X?) >>> True = 1 File "<stdin>", line 1 SyntaxError: can't assign to keyword
https://docs.python.org/3/reference/datamodel.html#the-standard-type-hierarchy https://docs.python.org/3/search.html?q=singleton - "Since None is a singleton, testing for object identity (using == in C) is sufficient. There is no PyNone_Check() function for the same reason." https://docs.python.org/3/c-api/none.html?highlight=singleton - "Using a trailing comma for a singleton tuple: a, or (a,)" (?) https://docs.python.org/3/library/stdtypes.html?highlight=singleton#tuple https://docs.python.org/3/library/stdtypes.html#boolean-values https://docs.python.org/3/library/stdtypes.html#truth-value-testing In Python 2: >>> True True >>> True is True True >>> True = 1 >>> True is 1 True >>> True is None False >>> True = None >>> True is None True On Mon, Mar 18, 2019 at 7:34 AM Chris Angelico <ros...@gmail.com> wrote: > On Mon, Mar 18, 2019 at 10:14 PM Juancarlo Añez <apal...@gmail.com> wrote: > > > > It came to my attention that: > > > > In the original PEP True and False are said to be singletons > https://www.python.org/dev/peps/pep-0285/, but it's not in the Data Model > https://docs.python.org/3/reference/datamodel.html > > > > > > This came to my attention by code wanting to own the valid values in a > dict's key: > > > > if settings[MY_KEY] is True: > > ... > > > > > > If True and False are singletons in the spec (and not only in the > CPython implementation), it should be prominent and well known. > > > > "Singleton" technically means that there is only one such object. > 'None' is a singleton, by language specification; if type(x) is > type(None), you can safely assume that x is None. Booleans are a bit > more tricky; there will only ever be those two, but they're two. IMO > the PEP is minorly inaccurate to use the word "singleton" there, but > it's no big deal. As Remi says, the two built-in ones are the only two > instances of that type. > > ChrisA > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
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