Question

Is there a more pythonic way to write __getitem__ than the following? The issue is checking type and doing different things depending on the type of the parameter in the call.

class This():
    def __init__(self, name, value):
        self.name, self.value = name, value

class That():
    def __init__(self):
        self.this_list = []
    def add_this(self, this):
        self.this_list.append(this)
    def __getitem__(self, x):
        if isinstance(x, int):
            return self.this_list[x] # could wrap in try/except for error checking
        elif isinstance(x, str):
            for this in self.this_list:
                if this.name == x:
                    return this
            return None


a = This('a', 1)
b = This('b', 2)
c = That()
c.add_this(a)
c.add_this(b)
print c[1].name
print c['a'].name

Answer 1

There are quite a few options, but I think there is not one best choice. It depends on your use case and preferences. Just to give you a few hints:

Do you really have to store the data in a list? In your example you could use a dictionary and insert the object twice: Once using the integer as key and once using the string as a key. That would make your __getitem__ quite simple. 😉

Another option would be to make your interface more explicit and use byInt/byString methods. You should choose better names of course.

If you give more details about what you really want to do, I could propose more alternatives.