How can I create an object and add attributes to it?

Question

I want to create a dynamic object (inside another object) in Python and then add attributes to it.

I tried:

obj = someobject
obj.a = object()
setattr         


        

Answer 1

There is types.SimpleNamespace class in Python 3.3+:

obj = someobject
obj.a = SimpleNamespace()
for p in params:
    setattr(obj.a, p, value)
# obj.a.attr1

collections.namedtuple, typing.NamedTuple could be used for immutable objects. PEP 557 -- Data Classes suggests a mutable alternative.

For a richer functionality, you could try attrs package. See an example usage.

Answer 2

The mock module is basically made for that.

import mock
obj = mock.Mock()
obj.a = 5

Answer 3

Which objects are you using? Just tried that with a sample class and it worked fine:

class MyClass:
  i = 123456
  def f(self):
    return "hello world"

b = MyClass()
b.c = MyClass()
setattr(b.c, 'test', 123)
b.c.test

And I got 123 as the answer.

The only situation where I see this failing is if you're trying a setattr on a builtin object.

Update: From the comment this is a repetition of: Why can't you add attributes to object in python?

Answer 4

Now you can do (not sure if it's the same answer as evilpie):

MyObject = type('MyObject', (object,), {})
obj = MyObject()
obj.value = 42