Finding a list of all double-underscore variables

Where can I find a list of all double-underscore variables that are commonly used in Python?

In Python, variables starting and ending with double underscores are typically to store metadata or are built into the system. For example,

#!/usr/bin/env python

__author__ = 'Michael0x2a'
__license__ = 'GPL'

class Test(object):
    def __init__(self):
        print 'Hello World!'

if __name__ == '__main__':
    t = Test()

I'm pretty certain __author__ and __license__ are pretty well known. What other double-underscore metadata variables are there? Is there a comprehensive list I can check somewhere? Can I just make up my own, or are there a bunch of ones that have become de-facto standards that I should use?

Things like __init__, __name__, and __doc__ are pretty much built into Python. Are those the only reserved double-underscore variables? Are there any more? Is there some place I can get a list?

Related:

• What is the common header format of Python files?
• I need __closure__ (links to this mindmap of a bunch of double-underscore variables)

If you want to see magic names whether documented or not, go to the Lib directory and run:

egrep -oh '__[A-Za-z_][A-Za-z_0-9]*__' *.py | sort | uniq

That produces:

'__all__'
'__args__'
'__author__'
'__bases__'
'__builtin__'
'__builtins__'
'__cached__'
'__call__'
'__class__'
'__copy__'
'__credits__'
'__date__'
'__decimal_context__'
'__deepcopy__'
'__dict__'
'__doc__'
'__exception__'
'__file__'
'__flags__'
'__ge__'
'__getinitargs__'
'__getstate__'
'__gt__'
'__import__'
'__importer__'
'__init__'
'__ispkg__'
'__iter__'
'__le__'
'__len__'
'__loader__'
'__lt__'
'__main__'
'__module__'
'__mro__'
'__name__'
'__package__'
'__path__'
'__pkgdir__'
'__return__'
'__safe_for_unpickling__'
'__setstate__'
'__slots__'
'__temp__'
'__test__'
'__version__'