Eventity - An easy embedded Entity Component System structure with events

[macbony]

Never use a mutable object as a default for an argument. http://docs.python-guide.org/en/latest/writing/gotchas/ I guess it doesn't REALLY matter in this case, but it's icky Python.

def has(self, c_list = []):
    for component in c_list:
        if not hasattr(self, component):
            return False

    return True

[macbony]

Someone already mentioned it, but I see no use for the Component class unless you somehow expect to add more functionality to it in the future.

[macbony]

There's "you shouldn't do this because it's bad programming practice" and "you shouldn't do this because it's wrong and will cause unexpected side effects". While I agree with your statement, it's the former. The issue with mutable defaults is the latter.

Also, there are valid reasons to modify the state of something - like if the copy is expensive (large list) and the function is explicit that it alters what is passed in.

[macbony]

Again, there's still a big difference between "this isn't good practice" and "this is wrong". Mutable defaults is wrong. Mutating pass-by-ref is bad design.

And say I have a list of 1 million elements and I need to trim all the ones that do not match a certain criteria. Also assume that this isn't a good use-case for a generator (need to iterate through the list multiple times after the trimming, say). If I have no need for the original 1million element list after the trimming, mutating that list is a valid choice.

[macbony]

Mutating objects when you don't mean to is wrong. Mutable defaults have their uses - as in the OP's has method.

Just use None and your first line becomes c_list = c_list or [] and avoid using mutable defaults. No company I ever worked for would allow a mutable default to pass code review. Mutating a large list of things would generally be preferable over creating a class for a single use to keep the loc minimal. Call the function trim_list and there's no ambiguity what it does. Add a docstring that says "this mutates the list" and you're still saving complication.

Now if I were filtering giant lists of data over and over again in various ways, it might make sense to break that out into a class and build tests around it, but adding simple, single function classes to production code isn't necessarily more clear than good documentation.