In the first situation, Num2
is extending the class Num
and since you are not redefining the special method named __init__()
in Num2
, it gets inherited from Num
.
When a class defines an
__init__()
method, class instantiation automatically invokes__init__()
for the newly-created class instance.
In the second situation, since you are redefining __init__()
in Num2
you need to explicitly call the one in the super class (Num
) if you want to extend its behavior.
class Num2(Num): def __init__(self,num): Num.__init__(self,num) self.n2 = num*2
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