It happens most of the time that given a condition we need to decide whether a particular class should inherit a class or not, for example given a person, if he/she is eligible for an admission in a university only then they should be a student otherwise they should not be a student.
Let’s consider an example, where given a condition, we want a class (say C) to dynamically inherit from either class A or class B. We need to create two different classes C_A and C_B, which inherit from A and B respectively, However if the conditional inheritance is to either inherit or not based on a condition then we can use a different approach as discussed below
Example 1: Conditional Inheritance between 2 classes:
Create two classes C_A and C_B, and based on the condition return the respective class object.
Python3
class A(object): def __init__(self, x): self.x = x def getX(self): return self.X class B(object): def __init__(self, x, y): self.x = x self.y = y def getSum(self): return self.X + self.y # inherits from A class C_A(A): def isA(self): return True def isB(self): return False # inherits from B class C_B(B): def isA(self): return False def isB(self): return True # return required Object of C based on cond def getC(cond): if cond: return C_A(1) else: return C_B(1,2) # Object of C_A ca = getC(True) print(ca.isA()) print(ca.isB()) # Object of C_B cb = getC(False) print(cb.isA()) print(cb.isB()) |
Output:
True False False True
Example 2: For Either inheriting or not from A:
The approach is to use conditional statements while declaring the classes the given class C inherits. The below code executes and returns True
Python3
class A(object): def __init__(self, x): self.x = x def getX(self): return self.X # Based on condition C inherits # from A or it inherits from # object i.e. does not inherit A cond = True # inherits from A or B class C(A if cond else object): def isA(self): return True # Object of C_A ca = C(1) print(ca.isA()) |
Output:
True
Example 3: The following code won’t run, as C does not inherit from A, thus has a default constructor that does not take any argument
Python3
class A(object): def __init__(self, x): self.x = x def getX(self): return self.X # Based on condition C inherits from # A or it inherits from object i.e. # does not inherit A cond = False ## inherits from A or B class C(A if cond else object): def isA(self): return True # Object of C_A ca = C(1) print(ca.isA()) |
Output:
TypeError Traceback (most recent call last)
<ipython-input-16-f0efc5a814d9> in <module>
17
18 # Object of C_A
—> 19 ca = C(1)
20 print(ca.isA())
21TypeError: object() takes no parameters
