Dynamically set inheritance in Python

Question

I have class A that is supposed to inherit class B whose name is not yet known at the time of A being written. Is it possible to declare A not inheriting anything, and add B as the base class during A's instantiation? Example:

First file

class B:
  def __init__(self):
    self.__name = "Class B"

  def name(self):
    return self.__name

Second file

class A:
  def __init__(self):
    self.__name = "Class A"

# At some point here, the appropriate module name and location is discovered
import sys
sys.path.append(CustomModulePath)
B = __import__(CustomModuleName)

magic(A, B) # TODO What should magic() do?

a = A()
print a.name() # This will now print "Class A", since name() is defined in B.

In this application I need to manipulate classes based on the application-specific metadata, not by regular class names. — dpq
– dpq, Commented Jun 22, 2010 at 15:03

Community · Accepted Answer · 2017-05-23 12:01:12Z

2

Yeah, you can accomplish this with metaclasses. It's not the easiest topic to wrap your head around but it'll do the job. There's a Stack Overflow question about them that looks like it has some good information and I also found an IBM article that might help as well. Somewhere in the official Python documentation, there's a section about them but I can't recall exactly where offhand.

edited May 23, 2017 at 12:01

CommunityBot

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answered Jun 22, 2010 at 14:52

Rakis

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2 Comments

Claudiu Over a year ago

the SO question particularly has an example on how to mess with inheritance, so look there for sure

dpq Over a year ago

Looks like metaclasses are exactly what I needed, thanks a lot!

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