Pretty rare but not unheard of. I do know that most of the code bases I work in ...

guitarbill · on Oct 6, 2018

Not quite with ==, but there is precedence where operators with basic builtin types throw a TypeError when the operation doesn't make sense:

    >>> 0 > None
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: '>' not supported between instances of 'int' and 'NoneType'

wool_gather · on Oct 6, 2018

Absolutely; there's no good boolean answer for > when you have different types, so the `TypeError` is perfect there.

ubernostrum · on Oct 7, 2018

At the same time, this result is entirely dependent on the types involved. For example, "1.0 > 0" has a well-defined answer, and Python returns it.

Considering the expression "x > y", the full process is:

1. Call x.__gt__(y).

2. If that returns a bool, that's the result. If it raises an exception, propagate the exception.

3. If it returns the sentinel value NotImplemented, attempt the reflected version of the operation: y.__lt__(x).

4. If that returns a bool, that's the result. If it raises an exception, propagate the exception.

5. If it returns the sentinel value NotImplemented, raise TypeError and inform the programmer this operator is not valid on these types.