Python operator overloading for join

Question

I have a class which instances shall be presented as string if being used in the context of a string. To be precise, a attribute pointing to a string should be returned.

The class looks as the following and works so far:

class Test:
    string = ""

    def __init__(self, value=""):
        self.string = value

    def __repr__(self):
        return str(self.string)

    def __str__(self):
        return self.__repr__()

    def __add__(self, other):
        return "%s%s" % (self.string, other)

    def __radd__(self, other):
        return "%s%s" % (other, self.string)

Unfortunately, I get a TypeError when I try doing something like this:

>>> "-".join([Test("test"), Test("test2")])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: sequence item 0: expected string, instance found

Doing the same with a string, I get the expected result:

>>> "-".join(["test", "test"])
'test-test'
>>> 

I'm pretty sure I'm just missing the correct operator overload function. Could somebody how to achieve this with class instances in the list?

Thanks.

Answer 1

join requires elements to be strings, as documented here: https://docs.python.org/3/library/stdtypes.html#str.join

You need to explicitly convert your objects to strings, e.g.:

"-".join(map(str, [Test("test"), Test("test2")]))