Python's Class Inheritance

Question

# Defining a Base class to be shared among many other classes later:

class Base(dict):
    """Base is the base class from which all the class will derrive.
    """
    name = 'name'    
    def __init__( self):
        """Initialise Base Class
        """
        dict.__init__(self)
        self[Base.name] = ""

# I create an instance of the Base class:

my_base_instance = Base()

# Since a Base class inherited from a build in 'dict' the instance of the class is a dictionary. I can print it out with:

print my_base_instance   Results to: {'name': ''}


# Now I am defining a Project class which should inherit from an instance of Base class:

class Project(object):
    def __init__(self):
        print "OK"
        self['id'] = ''

# Trying to create an instance of Project class and getting the error:

project_class = Project(base_class)

TypeError: __init__() takes exactly 1 argument (2 given)

Answer 1

there are two mistakes in your code:

1) Class inheritance

class Project(Base):   # you should inherit from Base here...
    def __init__(self):
        print "OK"
        self['id'] = ''

2) Instance definition (your __init__ does not requires any explicit parameter, and for sure not the ancestor class)

project_class = Project() # ...and not here since this is an instance, not a Class

Answer 2

When you're instantiating a class, you don't need to pass in base_class. That's done at definition. __init__ takes exactly 1 argument, which is self, and automatic. You just need to call

project_class = Project()

Answer 3

For Project to inherit from Base, you should not subclass it from object but from Base i.e class Project(Base). You get TypeError: init() takes exactly 1 argument (2 given) error when you instantiate Project class because the constructor takes only 1 parameter(self) and you pass base_class too. 'self' is passed implicitly by python.