How To Fix “Typeerror: Cannot Create A Consistent Method Resolution Order (Mro)” In Python

When working with Python, it is usual to encounter mistakes. One such issue, “TypeError: Cannot create a consistent method resolution order (MRO),” might be very aggravating. This issue usually occurs when there is a dispute in the inheritance structure of classes. In this article, we will explore the causes of this error and provide effective solutions to resolve it.

What is “Typeerror: Cannot Create A Consistent Method Resolution Order (MRO)”?

The error message “TypeError: Cannot create a consistent method resolution order (MRO)” typically occurs in object-oriented programming languages, such as Python, when there is an issue with the class hierarchy and the method resolution order cannot be determined consistently.

Syntax :

Error "Typeerror: Cannot Create A Consistent Method Resolution Order (Mro)" 

Why does “Typeerror: Cannot Create A Consistent Method Resolution Order (MRO)” Occur?

Below, are the reasons for the occurrence of “Typeerror: Cannot Create A Consistent Method Resolution Order (Mro)” In Python.

Diamond Inheritance Problem

In this example, below code provided below defines three classes: A, B, and C. A and B are base classes, and C is a child class inheriting from both A and B. However, there’s a potential issue in the class hierarchy that might lead to the “TypeError: Cannot create a consistent method resolution order (MRO)” error.

Python

# Base class 1
class  A:
    def  a_method(self):
        print('A')

# Base class 2
class  B(A):
    def  b_method(self):
        print('B')

# Child class
class  C(A, B):
    def  c_method(self):
        print('C')

Output:

class  C(A, B): 
    ^^^^^^^^^^^^^^^
TypeError: Cannot create a consistent method resolution
order (MRO) for bases A, B

Approaches to Solve “Typeerror: Cannot Create A Consistent Method Resolution Order (Mro)”

Below, are the approahes to solve “Typeerror: Cannot Create A Consistent Method Resolution Order (Mro)”.

• Creating Second Base Class
• Remove First Class From Inherited List
• Rearrange Order of Class Inheritance

Creating Second Base Class

To use multiple inheritance from the Third class, just remove the first class from the second by changing Second(First) to Second(object), or simply Second.

Python

# Base class 1
class  A:
    def  a_method(self):
        print('A')

# Base class 2
class  B:
    def  b_method(self):
        print('B')

# Child class
class  C(A, B):
    def  c_method(self):
        print('C')

Remove First Class From Inherited List

below code defines three classes (A, B, and C). C inherits from B. No “TypeError: Cannot create a consistent method resolution order (MRO)” is likely as there is a clear and linear inheritance hierarchy without circular dependencies.

Python

# Base class 1
class  A(object):
    def  a_method(self):
        print('A')

# Base class 2
class  B(object):
    def  b_method(self):
        print('B')

# Child class
class  C(B):
    def  c_method(self):
        print('C')

Rearrange Order of Class Inheritance

One option to overcome the problem while keeping your code intact is to alter the order in which the class is inherited. By importing the Second Class before the First.

Python

# Base class 1
class  A:
    def  a_method(self):
        print('A')

# Base class 2
class  B(A):
    def  b_method(self):
        print('B')

# Child class
class  C(B, A):
    def  c_method(self):
        print('Print from Car class')

Conclusion

In conclusion , To resolve the “TypeError: Cannot create a consistent method resolution order (MRO)” in Python, carefully examine the class hierarchy for circular dependencies and inconsistent inheritance orders. Avoid circular references where a class directly or indirectly inherits from itself. Establish a clear and consistent order when inheriting from base classes in child classes, ensuring a logical and unambiguous method resolution order.