Comparing boolean values with ==
works in Python. But when I apply the boolean not
operator, the result is a syntax error:
Python 2.7 (r27:82500, Sep 16 2010, 18:02:00)
[GCC 4.5.1 20100907 (Red Hat 4.5.1-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> True == True
True
>>> False == False
True
>>> True is not False
True
>>> True == not False
File "<stdin>", line 1
True == not False
^
SyntaxError: invalid syntax
>>>
Why is this a syntax error? I would expect not False
to be an expression that returns a boolean value, and True == <x>
to be valid syntax wherever <x>
is an expression with valid syntax.
It has to do with operator precedence in Python (the interpreter thinks you're comparing True to not, since ==
has a higher precedence than not
). You need some parentheses to clarify the order of operations:
True == (not False)
In general, you can't use not
on the right side of a comparison without parentheses. However, I can't think of a situation in which you'd ever need to use a not
on the right side of a comparison.