Python None and if conditions

Question

I have some code here:

m = None
n = None

if not m:
    print "Something happens"
>>> Something happens

if I do:

if not m and n:
    print "Something happens"

Nothing happens.

But I can do:

m, n = 1,2
if m and n:
    print "Something happens"
>>> Something happens

Why are if and if not handled the same way? Does 'if not', not take 'and' statements?

Thank you

Answer 1

You have an operator precedence problem.

if not m and n is equivalent to if (not m) and n. What you want is if not m and not n or if not (m or n).

_{See also: De Morgan's Laws}