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test_method_objects.py
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60 lines (45 loc) · 2.63 KB
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"""Class Definition Syntax.
@see: https://docs.python.org/3/tutorial/classes.html#method-objects
Classes can have two types of attribute references: data or methods. Class methods are called
by [variable_name].[method_name]([parameters]) as opposed to class data which lacks the ().
"""
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