Extending builtin classes in python

Question

How can I extend a builtin class in python? I would like to add a method to the str class.
I\'ve done some searching but all I\'m finding is older posts, I\'m hoping s

Answer 1

Assuming that you can not change builtin classes. To simulate a "class reopening" like Ruby in Python3 where __dict__ is an mappingproxy object and not dict object :

def open(cls):
  def update(extension):
    for k,v in extension.__dict__.items():
      if k != '__dict__':
        setattr(cls,k,v)
    return cls
  return update


class A(object):
  def hello(self):
    print('Hello!')

A().hello()   #=> Hello!

#reopen class A
@open(A)
class A(object):
  def hello(self):
    print('New hello!')
  def bye(self):
    print('Bye bye')


A().hello()   #=> New hello!
A().bye()     #=> Bye bye

I could also write a decorator function 'open' as well:

def open(cls):
  def update(extension):
    namespace = dict(cls.__dict__)
    namespace.update(dict(extension.__dict__))
    return type(cls.__name__,cls.__bases__,namespace)
  return update