What is the meaning of three dots (...) in Python code and where can I see the full body of code?

Question

This is the code of the atan and tan functions in the math module in Python. Their body consist of three dots (...). Many built-in functions also do the same. What is the meaning of that and where can I see the full body instead of three dots?

def tan(__x: _SupportsFloatOrIndex) ->float: ...

def atan(__x: _SupportsFloatOrIndex) ->float: ...

Does this answer your question? [Where are math.py and sys.py?](https://stackoverflow.com/questions/18857355/where-are-math-py-and-sys-py) — Jan Wilamowski, Jan 06 '22 at 06:12

Sy Ker · Answer 1 · 2022-01-06T06:35:37.300

It's the Ellipsis, it has many meanings and none at all. Let me explain;

It's an 'empty' singleton object with no method and its interpretation is purely up to whatever implements the __getitem__ function and sees Ellipsis objects there.

It can be used as a substitute for pass or not yet implemented code;

def my_function(arg): 
    ...

It is used to denote certain types to a static type checker when using the typing module (for type hints).

def partial(func: Callable[..., str], *args) -> Callable[..., str]:
    # code

In slice syntax to represent the full slice in remaining dimensions;

import numpy as np
>>>   
>>> array = np.random.rand(2, 2, 2, 2)
>>> print(array[..., 0])

[[[0.03265588 0.85912865]
  [0.45491733 0.3654667 ]]

 [[0.58577745 0.11642329]
  [0.88552571 0.69755581]]]

Thank you so much for this question, I learned something new in Python today.

score 6 · Answer 2 · edited Nov 01 '22 at 14:27

It seems you dug into the math library.

Actually, the file you are referencing is a Python module written in C. In order to add type-hints to that file (which is an "Extension Module" as it is written in C), the type hints are added to a "stub" file with the extension .pyi.

Type-hints are added via a stub-file *.pyi.

Here the ellipsis (...) is part of the syntax, so the code-block below really shows the complete file contents.

Here is a detailed explanation: What is the use of stub files (.pyi ) in python?

What is the meaning of three dots (...) in Python code and where can I see the full body of code?

2 Answers2