Why is object.__getattr__ missing?

Question

Why does object seem not to have a __getattr__ method? It defines both __setattr__ and __delattr__. Doesn't it need all three?

>>> object.__setattr__
<slot wrapper '__setattr__' of 'object' objects>
>>> 
>>> object.__delattr__
<slot wrapper '__delattr__' of 'object' objects>
>>> 
>>> object.__getattr__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'object' has no attribute '__getattr__'
>>> sys.version
'2.7.3 (default, Feb 27 2014, 19:58:35) \n[GCC 4.6.3]'

Answer 1

Indeed, object does not have a __getattr__ method.

>>> import pprint
>>> pprint.pprint(dir(object))
['__class__',
 '__delattr__',
 '__doc__',
 '__format__',
 '__getattribute__',
 '__hash__',
 '__init__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__']

Instead, it has __getattribute__.

>>> object.__getattribute__
<slot wrapper '__getattribute__' of 'object' objects>

https://docs.python.org/2/reference/datamodel.html#object.__getattribute__ explains why:

object.__getattribute__(self, name)

Called unconditionally to implement attribute accesses for instances of the class. If the class also defines __getattr__(), the latter will not be called unless __getattribute__() either calls it explicitly or raises an AttributeError.

In other words, if you have __getattribute__, it doesn't make sense to also define __getattr__.

Historically, __getattr__ came first, and __getattribute__ was introduced with "new-style classes" in Python 2.3 (iirc). Python 3 only has new-style classes but seems to have preserved both hooks anyway (perhaps because it can be convenient to have a hook that is only called if "normal attribute access" fails).

Answer 2

__getattr__ is a method that runs only after __getattribute__. Since object has the latter, there is technically no need for the former. But in general, you shouldn’t expect object to have all the things that other objects (deriving from it) have. Since object is implemented in native code, it may behave a bit differently.