ellipsis

Properties

>>> dir(...)
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']

Definition

The ellipsis literal, written as ..., is a built-in singleton object of type ellipsis.
It is commonly used as a placeholder to indicate omitted code, incomplete logic, or “this will be implemented later.”

def future_function():
    ...

class MyClass:
    def method(self):
        ...

Using ellipsis

Placeholder for incomplete code

... is often used instead of pass when you want to clearly signal that something is intentionally left unfinished.

def future_function():
    ...

class MyClass:
    def method(self):
        ...

In type hints

Ellipsis can be used in type hints to indicate variadic arguments or incomplete type information:

from typing import Tuple

def process(*args: int) -> Tuple[int, ...]:
    ...

# In function signatures
def func(x: int, ...) -> None:
    ...

In slicing operations (NumPy and other libraries)

Some libraries, particularly NumPy, interpret ... in slicing operations to mean "all remaining dimensions":

import numpy as np

arr = np.array([[[1, 2], [3, 4]], [[5, 6], [7, 8]]])
arr[..., 0]  # Selects the first element along the last dimension

Singleton behavior

Every occurrence of ... refers to the same singleton object:

>>> ... is Ellipsis
True

>>> ... is ...
True

>>> type(...)
<class 'ellipsis'>

>>> id(...) == id(Ellipsis)
True

Boolean value

Ellipsis is truthy:

>>> bool(...)
True

>>> if ...:
...     print("Ellipsis is truthy")
Ellipsis is truthy

Dunder methods

Dunder Method	Operation	Example (normal syntax)	Example (dunder call)
__repr__	Object representation	repr(...) → 'Ellipsis'	....__repr__()
__str__	String conversion	str(...) → 'Ellipsis'	....__str__()
__bool__	Truth value	bool(...) → True	....__bool__()
__eq__	Equality comparison	... == Ellipsis → True	....__eq__(Ellipsis)
__ne__	Inequality comparison	... != None → True	....__ne__(None)
__hash__	Hash value	hash(...)	....__hash__()
__lt__	Less than	... < Ellipsis → False	....__lt__(Ellipsis)
__le__	Less than or equal	... <= Ellipsis → True	....__le__(Ellipsis)
__gt__	Greater than	... > Ellipsis → False	....__gt__(Ellipsis)
__ge__	Greater than or equal	... >= Ellipsis → True	....__ge__(Ellipsis)