Finding a list of all double-underscore variables?


Related: What is the common header format of Python files?

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?

I was browsing and encountered another question that linked to a mindmap of a bunch of double-underscore variables.

Asked By: Michael0x2a



The complete list used by Python is given in the Python Language Reference section 3, “Data model”. Every other one is non-standard or used by third-party modules and is documented separately.

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:

Answered By: Raymond Hettinger

when i use


i got these:

'__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__has
h__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__'
, '__setattr__', '__sizeof__', '__str__', '__subclasshook__'

and i think they are the dunder names every object will have in python

Answered By: atongsa
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