learn-python/src/classes/test_method_objects.py at master · DevOps-UA/learn-python · GitHub

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"""Class Definition Syntax.

@see: https://docs.python.org/3/tutorial/classes.html#method-objects

"""

class MyCounter:

"""A simple example of the counter class"""

counter = 10

def get_counter(self):

"""Return the counter"""

return self.counter

def increment_counter(self):

"""Increment the counter"""

self.counter += 1

return self.counter

def test_method_objects():

"""Method Objects."""

# The other kind of instance attribute reference is a method. A method is a function that

# “belongs to” an object. (In Python, the term method is not unique to class instances: other

# object types can have methods as well. For example, list objects have methods called append,

# insert, remove, sort, and so on. However, in the following discussion, we’ll use the term

# method exclusively to mean methods of class instance objects, unless explicitly stated

# otherwise.)

# But be aware that counter.get_counter() is not the same thing as MyCounter.get_counter() —

# it is a method object, not a function object.

# Usually, a method is called right after it is bound

counter = MyCounter()

assert counter.get_counter() == 10

# However, it is not necessary to call a method right away: counter.get_counter() is a method

# object, and can be stored away and called at a later time. For example:

get_counter = counter.get_counter

assert get_counter() == 10

# What exactly happens when a method is called? You may have noticed that counter.get_counter()

# was called without an argument above, even though the function definition for get_counter()

# specified an argument (self). What happened to the argument? Surely Python raises an

# exception when a function that requires an argument is called without any — even if the

# argument isn’t actually used…

# Actually, you may have guessed the answer: the special thing about methods is that the

# instance object is passed as the first argument of the function. In our example, the call

# counter.get_counter() is exactly equivalent to MyCounter.get_counter(counter). In general,

# calling a method with a list of n arguments is equivalent to calling the corresponding

# function with an argument list that is created by inserting the method’s instance object

# before the first argument.

assert counter.get_counter() == 10

assert MyCounter.get_counter(counter) == 10

learn-python/src/classes/test_method_objects.py at master · DevOps-UA/learn-python · GitHub

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