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"""Class Definition Syntax.

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

After defining the class attributes to a class, the class object can be created by assigning the

object to a variable. The created object would have instance attributes associated with it.

"""

def test_class_objects():

"""Class Objects.

Class objects support two kinds of operations:

- attribute references

- instantiation.

"""

# ATTRIBUTE REFERENCES use the standard syntax used for all attribute references in

# Python: obj.name. Valid attribute names are all the names that were in the class’s namespace

# when the class object was created. For class MyCounter the following references are valid

# attribute references:

class ComplexNumber:

"""Example of the complex numbers class"""

real = 0

imaginary = 0

def get_real(self):

"""Return real part of complex number."""

return self.real

def get_imaginary(self):

"""Return imaginary part of complex number."""

return self.imaginary

assert ComplexNumber.real == 0

# __doc__ is also a valid attribute, returning the docstring belonging to the class

assert ComplexNumber.__doc__ == 'Example of the complex numbers class'

# Class attributes can also be assigned to, so you can change the value of

# ComplexNumber.counter by assignment.

ComplexNumber.real = 10

assert ComplexNumber.real == 10

# CLASS INSTANTIATION uses function notation. Just pretend that the class object is a

# parameterless function that returns a new instance of the class. For example

# (assuming the above class):

complex_number = ComplexNumber()

assert complex_number.real == 10

assert complex_number.get_real() == 10

# Let's change counter default value back.

ComplexNumber.real = 10

assert ComplexNumber.real == 10

# The instantiation operation (“calling” a class object) creates an empty object. Many classes

# like to create objects with instances customized to a specific initial state. Therefore a

# class may define a special method named __init__(), like this:

class ComplexNumberWithConstructor:

"""Example of the class with constructor"""

def __init__(self, real_part, imaginary_part):

self.real = real_part

self.imaginary = imaginary_part

def get_real(self):

"""Return real part of complex number."""

return self.real

def get_imaginary(self):

"""Return imaginary part of complex number."""

return self.imaginary

complex_number = ComplexNumberWithConstructor(3.0, -4.5)

assert complex_number.real, complex_number.imaginary == (3.0, -4.5)