On Mon, Jul 29, 2019 at 9:48 AM Michael Torrie <torr...@gmail.com> wrote: > > On 7/28/19 5:55 AM, Jonathan Moules wrote: > > But this appears to be explicitly called out as being "Worse" in PEP8: > > > > """ > > Don't compare boolean values to True or False using ==. > > > > Yes: if greeting: > > No: if greeting == True: > > Worse: if greeting is True: > > """ > > Yet the recommended solution to the problem of wanting a default > argument of an empty list is something like this: > > def foo(bar=False); > if bar is False: > bar = [] > > .... > > Clearly in this case the expression "not bar" would be incorrect.
This is a fairly unusual case, though. More commonly, the default would be None, not False, and "if bar is None:" is extremely well known and idiomatic. > There's a difference between looking for a particular identity or > sentinel, and checking for truthiness or falsiness. > > So I guess it all depends on what you need to do. If you just need to > check truthiness, just do "if greeting" If you need to know if the > variable is some particular sentinel, use the "if greeting is whatever". This analysis is correct, but the situations where you *actually* want to know if something "is True" or "is False" are rare enough that PEP 8 doesn't need to mention them; whereas the case where you actually just need the truthiness is so common (and so often miswritten) that it's worth being clear on it. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
