Python-2.5.1/Objects/object.c:PyObject_Dir を Python に変換するとこんな感じ↓

import sys
from types import *
def dir(object=object()):
"""This is an implementation of __builtins__.dir in pure Python."""
result = getattr(object, '__dict__', dict())
if object is dir.func_defaults[0]:
frame = sys._getframe(1)
result = frame.f_locals
elif isinstance(object, ModuleType):
pass
elif isinstance(object, (TypeType, ClassType, )):
result = set(result)
for base in object.__bases__:
result.update(dir(base))
else:
result = set(result)
# backward compatibility ?
result.update(getattr(object, '__members__', ()))
result.update(getattr(object, '__methods__', ()))
if hasattr(object, '__class__'):
result.update(dir(object.__class__))
result = list(result)
result.sort()
return result

C で書こうが Python で書こうがどうにでもなるのが Pythonic なところか。