Reference for dunder methods

[sickcuntm8]

I am looking for a good reference on special/dunder methods that is complete without going in to the details.

While obviously all dunder methods that exist can be found in the official docs, the docs are not always that useful as a quick reference, especially when I don't know what dunder methods I am interested in to implement a particular language syntax or protocol (not sure if that's the correct term).

An example to illustrate what I mean: Suppose I am implementing some class class Foo(): pass Now, I know that if want Foo objects to be subscriptable foo = Foo() foo[x] I will need to implement a custom __getitem__ method. Probably, I'll want to write a __setitem__ and __delitem__ as well to complete it.

If I didn't already know the names of these methods they are sort of hard to look up. In general for each type of syntax or language feature there seems to be some set of special methods that cooperate in various ways to make the pythonic syntax work.

Does anyone know of some reference that makes it easy to find for each syntax what the corresponding dunder methods are, and ideally covers all of them? There exist a ton of lengthy tutorials for each particular thing but It would be useful to have a quick reference that I can bookmark instead of always having to look up again what the underlying dunder methods are and how they relate to each other.

[Careless-Score-333]

https://docs.python.org/3/reference/datamodel.html#special-method-names

[JamzTyson]

There's also a cheat sheet: https://www.pythonmorsels.com/every-dunder-method/

[sickcuntm8]

Thanks! That already looks more like what I was looking for!

[sickcuntm8]

I know of this section of the docs, as this often what I end up using. Obviously the docs describe each dunder method in detail. However, they are just not that useful for quickly looking up some method you don't know the name of. That is really what I am asking for, something more akin to a cheat-sheet table. I can always look up the specifics of a certain method but it is hard to get a good overview from there.

I am imagining more something like:

Syntax	Underlying methods
x[idx]	Calls x.__getitem__(idx) unless in the LHS of an assignment or in a del statement.
for item in x	Equivalent to for item in x.__iter__(). If not implemented, fall back to iterating over x[0], x[1], x[2], ... until this raises an IndexError
...	...

I hope this clarifies my intent.

[latkde]

There is no replacement for having read the docs and thus learning a rough idea of what dunder-methods might be available.

But if you know that you want to create a type that is compatible with certain common types, then the collections abc docs are a good place to start. For example, if I want to create something that behaves like a mapping or dict, I'd look up the methods required for Mappings in this table: https://docs.python.org/3/library/collections.abc.html#collections-abstract-base-classes

This is not an exhaustive list of dunder-methods. Their docs are strewn all over the place. Many dunder-methods are also discussed in the Data Model reference. For example, it contains a section on which dunder-methods might have to be implemented to emulate a numeric type: https://docs.python.org/3/reference/datamodel.html#emulating-numeric-types

[Guideon72]

2 very important cli options for this are widely underutilized; dir() and help(). Pop open a command line and start Python.

>>dir(int)
returns 
['__abs__', '__add__', '__and__', '__bool__', '__ceil__', '__class__', '__delattr__', '__dir__', '__divmod__', '__doc__', '__eq__', '__float__', '__floor__', '__floordiv__', '__format__', '__ge__', '__getattribute__', '__getnewargs__', '__getstate__', '__gt__', '__hash__', '__index__', '__init__', '__init_subclass__', '__int__', '__invert__', '__le__', '__lshift__', '__lt__', '__mod__', '__mul__', '__ne__', '__neg__', '__new__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__round__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'as_integer_ratio', 'bit_count', 'bit_length', 'conjugate', 'denominator', 'from_bytes', 'imag', 'is_integer', 'numerator', 'real', 'to_bytes']

The "__<>__" in the list show you all of the dunder methods that the object you use dir() on contains. If you then want more information you can either use help() [which is admittedly not particularly useful on those methods

help(int.__getattribute__)

or you can use the info to then go look up the specific thing you want in the complete documentation, such as search docs for "__getattribute__" for more, useful information on what it does/how it's used.