Question

Unless I’m crazy if None not in x and if not None in x are equivalent. Is there a preferred version? I guess None not in is more english-y and therefore more pythonic, but not None in is more like other language syntax. Is there a preferred version?

Answer 1

They compile to the same bytecode, so yes they are equivalent.

>>> import dis
>>> dis.dis(lambda: None not in x)
  1           0 LOAD_CONST               0 (None)
              3 LOAD_GLOBAL              1 (x)
              6 COMPARE_OP               7 (not in)
              9 RETURN_VALUE
>>> dis.dis(lambda: not None in x)
  1           0 LOAD_CONST               0 (None)
              3 LOAD_GLOBAL              1 (x)
              6 COMPARE_OP               7 (not in)
              9 RETURN_VALUE

The documentation also makes it clear that the two are equivalent:

x not in s returns the negation of x in s.

As you mention None not in x is more natural English so I prefer to use this.

If you write not y in x it might be unclear whether you meant not (y in x) or (not y) in x. There is no ambiguity if you use not in.