Ulli Horlacher wrote: > Chris Angelico <ros...@gmail.com> wrote: >> On Sun, Jan 17, 2016 at 8:51 PM, Ulli Horlacher >> <frams...@rus.uni-stuttgart.de> wrote: >> > I have seen at several places "x == None" and "x is None" within >> > if-statements. >> > What is the difference? >> > Which term should I prefer and why? >> >> tl;dr: Prefer "x is None" as a check. > > And for the negation? > "if not x is None" or "if x is not None" > > I have seen the last one several times, but i do not understand it, > because: > >>>> x=0 >>>> x is not None > True >>>> not None > True >>>> x is True > False
- "is" has higher precedence than "not" - "is not" is an operator in its own right. So the evaluation is not (x is None) x (is not) None https://docs.python.org/dev/library/stdtypes.html#comparisons https://docs.python.org/dev/reference/expressions.html#operator-precedence -- https://mail.python.org/mailman/listinfo/python-list
