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Comment by dfinninger | Hacker News Reader

Just to discuss one point:

> And why are some classes (int, str, float) allowed to be lower case

Also, boolean. These are primitive data types. For instance, in Java there's a difference between int and Integer. I'd assume that Python special-cases these because they are primitive. But I haven't been through the Python internals, so it's only a guess.

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It's just for historical/ backwards compatibility reasons. These types have been part of Python from before it had classes. Today, they are classes and can be subclassed, etc, but too much code relies on their existing names to change them to match the modern convention.

They are far less primitive than Java's - they are classes too, but can't be extended.

I'm not sure which language did you mean there, but in Python those classes can be extended.

Also, the main reasons for special cases are historical; also, they predate PEP8 by a long time.

Sorry. That's something that was true in 2.x but not anymore. There used to be UserString, UserList, UserDict classes for serving as base classes. We still have those, but, at least now, we can extend the fundamental classes directly.

They are a bit more convenient than the built-ins.

We can inherit from `list`, `dict` etc., but objects of those classes are still not as flexible as "normal" objects. For example, we can't add an attribute to a list using `l = []; l.a = 1`.

I believe that makes them the same as any other class defined with `__slots__`:

    >>> class Foo:
    ...   __slots__ = ('a', 'b')
    ...
    >>> f = Foo()
    >>> f.a = 1
    >>> f.b = 2
    >>> f.c = 3
        Traceback (most recent call last):
          File "<stdin>", line 1, in <module>
        AttributeError: 'Foo' object has no attribute 'c'

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