Built-in magic variable names/attributes

Alas, the Data Model document is the most complete thing I can think of, and it's not even really designed as an index. I'm not entirely clear on what you're looking for, though; __all__ is a module global, __slots__ is a class attribute, __weakref__ only appears as a string inside the slot list, and __module__ is a function attribute et al. I guess any special attribute that's not typically callable, then?

Of course, you can always ask Python.

>>> dir(type)
['__abstractmethods__', '__base__', '__bases__', '__basicsize__', '__call__', '__class__', '__delattr__', '__dict__', '__dictoffset__', '__dir__', '__doc__', '__eq__', '__flags__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__instancecheck__', '__itemsize__', '__le__', '__lt__', '__module__', '__mro__', '__name__', '__ne__', '__new__', '__prepare__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasscheck__', '__subclasses__', '__subclasshook__', '__weakrefoffset__', 'mro']
>>> import sys
>>> dir(type(sys))
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']

At a glance you're definitely missing __mro__ and __subclasses__. Complicating this somewhat is that there are some special methods only used by code that happens to be built into Python, rather than by the core language: examples include __format__ (used by str.format) and the various ABC methods.

I don't even know what __weakrefoffset__ is.

Note that Python 3 has a handful of new things: there's a __prepare__ method used by metaclass shenanigans, functions and methods now use magic names for their attributes rather than noise like im_self (see the "User-defined functions" section of Data Model), and there's a __qualname__ on both modules and classes.

Also, the importing PEP mentions exactly what a module loader should do, including set some magic attributes: __name__, __file__, __path__, __loader__, and __package__.

import gc

print("\n".join(sorted({attrname for item in gc.get_objects() for attrname in dir(item) if attrname.startswith("__")})))
#>>> __about__
#>>> __abs__
#>>> __abstractmethods__
#>>> __add__
#>>> __all__
#>>> __and__
#>>> __annotations__
#>>> __author__
#>>> __base__
#>>> __bases__
#>>> __basicsize__
#>>> __bool__
#>>> __build_class__
#>>> __builtins__
#>>> __cached__
#>>> __call__
#>>> __cause__
#>>> __ceil__
#>>> __class__
#>>> __closure__
#>>> __code__
#>>> __complex__
#>>> __concat__
#>>> __contains__
#>>> __context__
#>>> __copy__
#>>> __copyright__
#>>> __credits__
#>>> __date__
#>>> __debug__
#>>> __deepcopy__
#>>> __defaults__
#>>> __del__
#>>> __delattr__
#>>> __delete__
#>>> __delitem__
#>>> __dict__
#>>> __dictoffset__
#>>> __dir__
#>>> __displayhook__
#>>> __divmod__
#>>> __doc__
#>>> __enter__
#>>> __eq__
#>>> __excepthook__
#>>> __exit__
#>>> __file__
#>>> __flags__
#>>> __float__
#>>> __floor__
#>>> __floordiv__
#>>> __format__
#>>> __func__
#>>> __ge__
#>>> __get__
#>>> __getattr__
#>>> __getattribute__
#>>> __getitem__
#>>> __getnewargs__
#>>> __getstate__
#>>> __globals__
#>>> __gt__
#>>> __hash__
#>>> __iadd__
#>>> __iand__
#>>> __iconcat__
#>>> __ifloordiv__
#>>> __ilshift__
#>>> __imod__
#>>> __import__
#>>> __imul__
#>>> __index__
#>>> __init__
#>>> __initializing__
#>>> __instancecheck__
#>>> __int__
#>>> __inv__
#>>> __invert__
#>>> __ior__
#>>> __ipow__
#>>> __irshift__
#>>> __isabstractmethod__
#>>> __isub__
#>>> __itemsize__
#>>> __iter__
#>>> __itruediv__
#>>> __ixor__
#>>> __kwdefaults__
#>>> __le__
#>>> __len__
#>>> __loader__
#>>> __lshift__
#>>> __lt__
#>>> __missing__
#>>> __mod__
#>>> __module__
#>>> __mro__
#>>> __mul__
#>>> __name__
#>>> __ne__
#>>> __neg__
#>>> __new__
#>>> __newobj__
#>>> __next__
#>>> __not__
#>>> __objclass__
#>>> __or__
#>>> __package__
#>>> __path__
#>>> __pos__
#>>> __pow__
#>>> __prepare__
#>>> __qualname__
#>>> __radd__
#>>> __rand__
#>>> __rdivmod__
#>>> __reduce__
#>>> __reduce_ex__
#>>> __repr__
#>>> __reversed__
#>>> __rfloordiv__
#>>> __rlshift__
#>>> __rmod__
#>>> __rmul__
#>>> __ror__
#>>> __round__
#>>> __rpow__
#>>> __rrshift__
#>>> __rshift__
#>>> __rsub__
#>>> __rtruediv__
#>>> __rxor__
#>>> __self__
#>>> __set__
#>>> __setattr__
#>>> __setitem__
#>>> __setstate__
#>>> __sizeof__
#>>> __slots__
#>>> __stderr__
#>>> __stdin__
#>>> __stdout__
#>>> __str__
#>>> __sub__
#>>> __subclasscheck__
#>>> __subclasses__
#>>> __subclasshook__
#>>> __suppress_context__
#>>> __traceback__
#>>> __truediv__
#>>> __trunc__
#>>> __version__
#>>> __weakref__
#>>> __weakrefoffset__
#>>> __wrapped__
#>>> __xor__