test_class_objects.py

"""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)