learn-python

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"""Class Definition Syntax.
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@see: https://docs.python.org/3/tutorial/classes.html#method-objects
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Classes can have two types of attribute references: data or methods. Class methods are called
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by [variable_name].[method_name]([parameters]) as opposed to class data which lacks the ().
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"""
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class MyCounter:
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    """A simple example of the counter class"""
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    counter = 10
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    def get_counter(self):
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        """Return the counter"""
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        return self.counter
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    def increment_counter(self):
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        """Increment the counter"""
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        self.counter += 1
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        return self.counter
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def test_method_objects():
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    """Method Objects."""
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    # The other kind of instance attribute reference is a method. A method is a function that
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    # “belongs to” an object. (In Python, the term method is not unique to class instances: other
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    # object types can have methods as well. For example, list objects have methods called append,
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    # insert, remove, sort, and so on. However, in the following discussion, we’ll use the term
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    # method exclusively to mean methods of class instance objects, unless explicitly stated
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    # otherwise.)
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    # But be aware that counter.get_counter() is not the same thing as MyCounter.get_counter() —
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    # it is a method object, not a function object.
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    # Usually, a method is called right after it is bound
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    counter = MyCounter()
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    assert counter.get_counter() == 10
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    # However, it is not necessary to call a method right away: counter.get_counter() is a method
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    # object, and can be stored away and called at a later time. For example:
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    get_counter = counter.get_counter
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    assert get_counter() == 10
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    # What exactly happens when a method is called? You may have noticed that counter.get_counter()
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    # was called without an argument above, even though the function definition for get_counter()
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    # specified an argument (self). What happened to the argument? Surely Python raises an
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    # exception when a function that requires an argument is called without any — even if the
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    # argument isn’t actually used…
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    # Actually, you may have guessed the answer: the special thing about methods is that the
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    # instance object is passed as the first argument of the function. In our example, the call
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    # counter.get_counter() is exactly equivalent to MyCounter.get_counter(counter). In general,
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    # calling a method with a list of n arguments is equivalent to calling the corresponding
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    # function with an argument list that is created by inserting the method’s instance object
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    # before the first argument.
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    assert counter.get_counter() == 10
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    assert MyCounter.get_counter(counter) == 10
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