What's the strange double underscored attribute (attribute) in Python?

Question

I see some strange but useful double underscored attribute in Python, such as:

__module__
__init__
__str__
__class__
__repr__
...

They seem to be some special attributes. What's the canonical name for them?

score 5 · Accepted Answer · answered Jan 10 '14 at 15:26

5

They are called Special Methods.

Python is a Duck Typed Language and many of the user-facing features of the language are implemented in "protocols" implemented by these special methods.

See: http://docs.python.org/release/2.5.2/ref/specialnames.html

As an Example:

To mimic comparison of arbitrary objects you implement the following two methods in your class:

__lt__
__eq__

answered Jan 10 '14 at 15:26

James Mills

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+1 for "Duck Typed", very informative! Thanks! – smwikipedia Jan 10 '14 at 15:32

score 2 · Answer 2 · answered Jan 10 '14 at 15:29

2

Per "Naming conventions" section of PEP-8

__double_leading_and_trailing_underscore__: "magic" objects or attributes that live in user-controlled namespaces. E.g. __init__, __import__ or __file__. Never invent such names; only use them as documented.

answered Jan 10 '14 at 15:29

vartec

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Man that PEP must be old! I think 50% of Pythonistas call them special methods the other other 50% magic methods :) – James Mills Jan 10 '14 at 15:31
Yup 13 years old this year! +1 on the "convention" used. – James Mills Jan 10 '14 at 15:32
@JamesMills: right, the original is old, but it's kept up to date. `Last modified Fri, 01 Nov 2013.` – vartec Jan 10 '14 at 15:35

What's the strange double underscored attribute (__attribute__) in Python?

2 Answers2

What's the strange double underscored attribute (attribute) in Python?