To me it seems like a useful shortcut that means: >>> x == True and type(x) == bool
But, as you say, it is best to just let the Python interpreter treat it as a boolean (i.e. within an `if`, it is converted automatically) Now, I am thinking it would actually be *bad* to have the CPython implementation define `inf` singletons -- imagine a 3rd party library (for example, sympy) that defines '==' for new types: ``` >>> from sympy import oo >>> oo == inf True >>> oo is inf False ``` Again, it would be useful for a shortcut: `x is inf` is the same as `x == inf and type(x) == float`, but with 3rd party libraries I don't think it's something good to rely on. On Mon, Sep 14, 2020, 12:05 AM Steven D'Aprano <st...@pearwood.info> wrote: > On Mon, Sep 14, 2020 at 12:16:54PM +1000, Chris Angelico wrote: > > > (How often do people even use "x is True"?) > > Alas, that is a common idiom. For example: > > > https://stackoverflow.com/questions/50816182/pep-8-comparison-to-true-should-be-if-cond-is-true-or-if-cond > > It's possibly less common than it used to be now that PEP 8 warns > against it: > > https://www.python.org/dev/peps/pep-0008/ > > and so linters flag it. But I've seen it used by beginners and > experienced programmers alike. > > There is some justification for it in the case that you want to test > specifically for the True instance, being much shorter than: > > arbitrary_object == 1 and type(arbitrary_object) is bool > > but many people have a mental blindspot and write: > > > if flag is True: > true_condition() > else: > false_condition() > > > even when they know full well that flag is guaranteed to be a bool. > > I know that sometimes I catch myself doing the same. I recently > rediscovered some old Pascal code I write in the 1990s and sure enough, > I have "if flag == true" in that too. > > Of course we all know that it should be written: > > if flag is True is True: > ... > > except I never know when to stop: > > if flag is True is True is True is True is True is True is ... > > > *wink* > > > -- > Steve > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/45KTF4Z6EMXLSLN5PFXKS4QGIM3QEKGR/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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