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Python Dunders

A compilaton of all Python dunder definitions with some key attributes

Category

Start

End

Writable

Called

Returns

Usage

Package

URL

__ilshift__

x <<= y

__invert__

__irshift__

x >>= y

__ixor__

x ^= y

__lshift__

x << y

__rlshift__

y << x

__rrshift__

y >> x

__rshift__

x >> y

__annotations__

A dict containing annotations of parameters. The keys of the dict are the parameter names, and 'return' for the return annotation, if provided. For more information on working with this attribute, see Annotations Best Practices.

__call__

x()

__closure__

None or a tuple of cells that contain bindings for the function’s free variables. See below for information on the cell_contents attribute.

__code__

The code object representing the compiled function body.

__defaults__

A tuple containing default argument values for those arguments that have defaults, or None if no arguments have a default value.

__globals__

A reference to the dictionary that holds the function’s global variables — the global namespace of the module in which the function was defined.

__kwdefaults__

A dict containing defaults for keyword-only parameters.

__bool__

bool(x)

__bytes__

bytes(x)

__complex__

complex(x)

__float__

float(x)

__hash__

hash(x)

__int__

int(x)

__iter__

iter(x)

__nonzero__

Like __bool__

__cmp__

__eq__

x == y

__ge__

x >= y

__gt__

x > y

__instancecheck__

isinstance(y, x) Defined for x's metaclass

__le__

x <= y

__lt__

x < y

__ne__

x != y

__subclasscheck__

issubclass(y, x)

__subclasshook__

issubclass(y, x), called for x if x is derived from ABC

__enter__

with x:

__exit__

with x:

__del__

__del__ is a finalizer. It is called when an object is garbage collected which happens at some point after all references to the object have been deleted.

__delattr__

Called for A when calling del A.x

__delitem__

Called for A when calling del A[n] or A[n:n] in which case a slice object is given as key

__delslice__

__delete__

del X.y will call y's __delete__ (property)

__get__

X.y = Y(), X.y will call y's __get__ (property)

__set__

X.y = Y(), X.y = z will call y's __set__ (property)

__all__

module.__all__, decides what's exported by module

__bases__

Returns a list of classes that X has directly inherited from

__class__

type(x)[y]

__dict__

The namespace supporting arbitrary function attributes.

__doc__

The function’s documentation string, or None if unavailable; not inherited by subclasses.

__module__

The name of the module the function was defined in, or None if unavailable.

__name__

The function’s name.

__qualname__

The function’s qualified name.

__sizeof__

sys.getsizeof(x), Internal size in bytes

__slots__

__subclasses__

Returns a list of classes that directly inherited X

__contains__

x in y

__getitem__

A[n]

__getslice__

__index__

list[x] calls x.__index__

__len__

len(x), also called by bool(x), guessing it's cause empty iterables should return False

__length_hint__

Estimate of len if len(x) raises TypeError, defined in iterators

__missing__

class X(dict) X()["missing"] Only works for subclass of dict, called if key is missing

__next__

next(x)

__reversed__

reversed(x), if not defined then len and getitem will be used

__setitem__

A[n] = x

__setslice__

__and__

x & y

__iand__

x &= y

__ior__

x |= y

__or__

x | y

__rand__

y & x, used if y hasn't implemented it or if that returns NotImplementedError

__ror__

y | x, used if y hasn't implemented it or if that returns NotImplementedError

__rxor__

y ^ x, used if y hasn't implemented it or if that returns NotImplementedError

__xor__

x ^ y

__class_getitem__

X[n]

__dir__

dir(x)

__getattr__

Called for attrs that aren't already defined.

__getattribute__

Called unconditionally to implement attribute accesses for instances of the class.

__setattr__

A.y = x

__abs__

abs(x)

__add__

x + y

__ceil__

math.ceil(x)

__divmod__

divmod(x, y) -> (i, j)

__floor__

math.floor(x)

__floordiv__

x // y

__iadd__

x += y

__ifloordiv__

x //= y

__imod__

x %= y

__imul__

x *= y

__ipow__

x **= y

__isub__

x -= y

__itruediv__

x /= y

__mod__

x % y

__mul__

x * y

__neg__

-x

__pos__

__pow__

pow(x, y)

__radd__

y + x, used if y hasn't implemented it or if that returns NotImplementedError

__rdiv__

y / x, used if y hasn't implemented it or if that returns NotImplementedError

__rdivmod__

divmod(y, x), used if y hasn't implemented it or if that returns NotImplementedError

__rfloordiv__

y // x, used if y hasn't implemented it or if that returns NotImplementedError

__rmod__

y % x, used if y hasn't implemented it or if that returns NotImplementedError

__rmul__

y * x, used if y hasn't implemented it or if that returns NotImplementedError

__round__

round(x)

__rpow__

pow(y, x), used if y hasn't implemented it or if that returns NotImplementedError

__rsub__

y - x, used if y hasn't implemented it or if that returns NotImplementedError

__rtruediv__

y / x, used if y hasn't implemented it or if that returns NotImplementedError

__sub__

x - y

__truediv__

x / y

__trunc__

math.trunc(x), floors positive, ceils negative

__imatmul__

x @= y

__matmul__

x @ y

__rmatmul__

y @ x, used if y hasn't implemented it or if that returns NotImplementedError

__init__

cls()

__init_subclass__

class Y(X): called for X if something inherits it

__new__

Called before init to create object of class without parameters

__prepare__

Return namespace for metaclass

__set_name__

class Y: foo = X() Called for X, attr has to be defined within class scope

__getnewargs__

return a tuple of how to call __new__ with pickle.loads(str), positional only

__getnewargs_ex__

Like __getnewargs__ but key-word only

__getstate__

__dict__ is pickled if this isn't defined, otherwise return obj is pickled

__reduce__

Low level interface for pickling, alternative to __getstate__ and __setstate__. Takes no parameters

__reduce_ex__

Takes presedence over __reduce__, takes one integer as parameter (the protocol number)

__setstate__

Returns new __dict__ for unpickled obj

__format__

"{0}".format(4) or format(X)

__fspath__

os.fspath(x)

__repr__

repr(x)

__str__

str(x)

__aenter__

async with X():

__aexit__

async with X():

__aiter__

__anext__

__await__

Used by asyncio, usually not needed

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