Defining a class in Python

class Car:
    pass

class Car():
    pass

What is the difference between these two开发者_Python百科? and,

a = Car

a = Car()

also, what is the difference between these two above?

Best Regards

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the first statement, a = Car simply makes a an alias to Car class. So after you do that, you could do b = a() and it would be the same as b = Car()

Once you attach the () at the end, it makes python actually initialize the class (either __call__ or just initialize, but you don't have to worry about that), and a becomes whatever that's returned by Car(), in this case, it is the class instance.

As for the difference between class Car: and class Car():. The second one is invalid syntax (edit: before 2.5, I would still say it's kind of bad style as there's no reason for it to be there if you're not inheritting). The reason you have the brackets there is when you need to inherit another class.

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In the first snippet, the latter is invalid syntax in older versions of Python.

In the second snippet, the former binds a reference to the class, and the latter binds a reference to a new instance of the class.