Is there a Python equivalent for Scala’s Option or Either?

The pythonic way for a function to say “I am not defined at this point” is to raise an exception.

>>> int("blarg")
Traceback (most recent call last):
  ...
ValueError: invalid literal for int() with base 10: 'blarg'

>>> dict(foo=5)['bar']
Traceback (most recent call last):
  ...
KeyError: 'bar'

>>> 1 / 0
Traceback (most recent call last):
  ...
ZeroDivisionError: integer division or modulo by zero

This is, in part, because there’s no (generally useful) static type checker for python. A Python function cannot syntactically state, at compile time, that it has a particular codomain; there’s no way to force callers to match all of the cases in the function’s return type.

If you prefer, you can write (unpythonically) a Maybe wrapper:

class Maybe(object):
    def get_or_else(self, default):
        return self.value if isinstance(self, Just) else default

class Just(Maybe):
    def __init__(self, value):
        self.value = value

class Nothing(Maybe):
    pass

But I would not do this, unless you’re trying to port something from Scala to Python without changing much.