oop.py

# !/usr/bin/python3

class ClassWithMethod:
    def say_something(self):
        print("Elementary!")

class ClassWithField:
    def __init__(self, name):
        self.name = name

class ClassWithFieldAndMethod:
    def tellName(self):
        print(self.name)

class ClassWithPrivateFieldAndMethod:
    def setName(self, name):
        self.__name = name


class ClassWithParamaterInConstructor:
    def __init__(self, name):
        self.name = name

class ClassWithStaticField:
    field = 40
    def someMethod():
        pass
    
def main():
    objectWithMethod = ClassWithMethod()
    objectWithMethod.say_something()

    objectWithField = ClassWithField("Lestrade")
    print(objectWithField.name)

    objectWithFieldAndMethod = ClassWithFieldAndMethod()
    objectWithFieldAndMethod.name = "John Watson"
    objectWithFieldAndMethod.tellName()

    objectWithFieldAndMethod2 = ClassWithFieldAndMethod()
    objectWithFieldAndMethod2.name = "Sherlock Holmes"
    objectWithFieldAndMethod2.tellName()

    # you can add field on the fly...
    # ... to the object!
    objectWithFieldAndMethod2.age = 33 
    
    # you can do this only if field has been added:
    print(objectWithFieldAndMethod2.age)

    # this results in error!
    #print(objectWithFieldAndMethod.age)

    objectWithPrivateField = ClassWithPrivateFieldAndMethod()
    objectWithPrivateField.setName("Mary Watson")
    # you can not do this (error:)
    #print(objectWithPrivateField.__name)
    # but you can this:
    print(objectWithPrivateField._ClassWithPrivateFieldAndMethod__name)
    
    objectConstructedWithParam = ClassWithParamaterInConstructor("Moriarty")
    print(objectConstructedWithParam.name)

    stat1 = ClassWithStaticField()
    stat2 = ClassWithStaticField()
    stat2.field = 41
    print(stat1.field) # object's field default value is 40
    print(stat2.field) # this object's field value is 41
    print(stat1.field) # object's field default value is 40
    
    print(ClassWithStaticField.field) # static field value is still 40!
    ClassWithStaticField.field = 42
    print(ClassWithStaticField.field) # not anymore!


if __name__ == "__main__":
    main()