"""
 objects.py

 Some object examples in python.
 See ./objects.js for a comparison

 Jim Mahoney | cs.marlboro.college | MIT License | Jan 2019
"""

# --- a minimal object ------------

# First we have to define it with "class".
# Then we can make one (i.e. "instantiate it") with its constructor.
#
# Note that unlike some languages (e.g. Java), 
# we can create new attributes after the class has been defined.

class Minimal:                           # define the class
    """ A minimal class """
    pass

m = Minimal()                            # create an instance 

m.name = "John Min"                      # put some data into m
print("m.name is {}".format( m.name ))   # get that data out of m

# --- an object with a method ----------

# Methods must be declared with the class.
# The instance is referred to as "self" within the method, which is passed explicitly. 
# The method definition argument list must start with self, 
# but is not passed when the method is invoked.

class HasMethod:                        # define the method in the class
    def set_name(self, name):
        self.name = name

h = HasMethod()                         # create an instance

h.set_name('John')                      # invoke it
print("h.name is {}".format( h.name ))

# --- an object constructor -----------

# Python has a special __init__ method whose arguments 
# define what can be specified when the object is created.

class WithConstructor:                 # define the class
    def __init__(self, name, age):
        self.name = name
        self.age = age

wc = WithConstructor('Sally', 21)      # create an instance

print("wc's name is {} and age is {}".format( wc.name, wc.age ))

# --- inheritance ---------

class Parent:
    def __init__(self, value):
        self.value = value
    def double_value(self):
        return 2 * self.value

class Child(Parent):
    pass

kid = Child(3)
print("kid.value is {} and .double_value() is {}".format( 
        kid.value, kid.double_value() ))