Mocking class constructor default parameters in Python

问题

Is there a way to mock just the default parameters of a class constructor? For example, if I have this class:

  class A (object):
      def __init__(self, details='example'):
          self.details = details

Is there a way to a mock just the default value of the details argument, eg to details='test'?

回答1:

Surely this is simplest:

  class TestA (A):
      def __init__(self, details='test'):
          super(TestA, self).__init__(details)

If you're not able to use TestA without changing code elsewhere, then you could try something a bit more direct:

>>> A().details
'example'
>>> A.__old_init = A.__init__
>>> A.__init__ = lambda self, details='test': self.__old_init(details)
>>> A().details
'test'

If your willing to go that far, though, why not do it the tidy way?

class A (object):
    _DEFAULT_DETAILS = 'details'

    def __init__(self, details=None):
        if details is None:
            self.details = self._DEFAULT_DETAILS
        else:
            self.details = details

Now you can override the default value without resorting to any trickery:

A._DEFAULT_DETAILS = 'test'

回答2:

Would a new mock class do?

class Amock(A):
  def __init__(self, details='newdefault'):
      super(Amock, self).__init__(details=details)

来源：https://stackoverflow.com/questions/36704191/mocking-class-constructor-default-parameters-in-python