What does the Ellipsis object do?

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While idly surfing the namespace I noticed an odd looking object called Ellipsis, it does not seem to be or do anything special, but it's a globally available builtin.

After a search I found that it is used in some obscure variant of the slicing syntax by Numpy and Scipy... but almost nothing else.

Was this object added to the language specifically to support Numpy + Scipy? Does Ellipsis have any generic meaning or use at all?

D:\workspace\numpy>python
Python 2.4.4 (#71, Oct 18 2006, 08:34:43) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> Ellipsis
Ellipsis

This came up in another question recently. I'll elaborate on my answer from there:

Ellipsis is an object that can appear in slice notation. For example:

myList[1:2, ..., 0]

Its interpretation is purely up to whatever implements the __getitem__ function and sees Ellipsis objects there, but its main (and intended) use is in the numeric python extension, which adds a multidimensional array type. Since there are more than one dimensions, slicing becomes more complex than just a start and stop index; it is useful to be able to slice in multiple dimensions as well. E.g., given a 4x4 array, the top left area would be defined by the slice [:2,:2]:

>>> a
array([[ 1,  2,  3,  4],
       [ 5,  6,  7,  8],
       [ 9, 10, 11, 12],
       [13, 14, 15, 16]])

>>> a[:2,:2]  # top left
array([[1, 2],
       [5, 6]])

Extending this further, Ellipsis is used here to indicate a placeholder for the rest of the array dimensions not specified. Think of it as indicating the full slice [:] for all the dimensions in the gap it is placed, so for a 3d array, a[...,0] is the same as a[:,:,0] and for 4d, a[:,:,:,0], similarly, a[0,...,0] is a[0,:,:,0] (with however many colons in the middle make up the full number of dimensions in the array).

Interestingly, in python3, the Ellipsis literal (...) is usable outside the slice syntax, so you can actually write:

>>> ...
Ellipsis

Other than the various numeric types, no, I don't think it's used. As far as I'm aware, it was added purely for numpy use and has no core support other than providing the object and corresponding syntax. The object being there didn't require this, but the literal "..." support for slices did.

What does the Ellipsis object do?, This came up in another question recently. I'll elaborate on my answer from there: Ellipsis is an object that can appear in slice notation. Examples of ellipsis in a Sentence. “Begin when ready” for “Begin when you are ready” is an example of ellipsis. Recent Examples on the Web. The words are memorialized on a mural of a bloodied, victorious Diaz painted on the side of a building in his hometown, the last word replaced by an ellipsis.

In Python 3, you can use the Ellipsis literal ... as a "nop" placeholder for code:

def will_do_something():
    ...

This is not magic; any expression can be used instead of ..., e.g.:

def will_do_something():
    1

(Can't use the word "sanctioned", but I can say that this use was not outrightly rejected by Guido.)

What does the Python Ellipsis object do?, While idly surfing the namespace I noticed an odd looking object called Ellipsis it does not seem to be or do anything special but its a Note that functions that use ellipsis must have at least one non-ellipsis parameter. Any arguments passed to the function must match the argument_list parameters first. The ellipsis (which are represented as three periods in a row) must always be the last parameter in the function. The ellipsis capture any additional arguments (if there are any).

As of Python 3.5 and PEP484, the literal ellipsis is used to denote certain types to a static type checker when using the typing module.

Example 1:

Arbitrary-length homogeneous tuples can be expressed using one type and ellipsis, for example Tuple[int, ...]

Example 2:

It is possible to declare the return type of a callable without specifying the call signature by substituting a literal ellipsis (three dots) for the list of arguments:

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

[ , …, ] (ellipsis) - Python Reference (The Right Way), Ellipsis is used for slicing multidimensional numpy arrays. 11], [13, 15]]) >>> # also Ellipsis object can be used interchangeably >>> n[1, Ellipsis, 1] array([[ 9,  What does ellipsis mean? ellipsis is defined by the lexicographers at Oxford Dictionaries as The omission from speech or writing of a word or words that are superfluous or able to be understood from contextual

You can also use the Ellipsis when specifying expected doctest output:

class MyClass(object):
    """Example of a doctest Ellipsis

    >>> thing = MyClass()
    >>> # Match <class '__main__.MyClass'> and <class '%(module).MyClass'>
    >>> type(thing)           # doctest:+ELLIPSIS
    <class '....MyClass'>
    """
    pass

What do the '…' dots mean in Python?, It is an object in Python called Ellipsis, whatever that means. It doesn't do anything AFAIK. Use it however you want (for example, as a placeholder for something  You are working on a Python script that relies heavily on the cos and sin functions of the math module. As these are the only functions you require, what should you do to import only these functions, rather than the whole math module?

From the Python documentation:

This object is used by extended slice notation (see the Python Reference Manual). It supports no special operations. There is exactly one ellipsis object, named Ellipsis (a built-in name).

[100% Working Code], Ellipsis is an object that can occur in slice notation. For example: myList[1:2, , 0]. Its interpretation is only up to no matter implements the  Spread syntax allows an iterable such as an array expression or string to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected, or an object expression to be expanded in places where zero or more key-value pairs (for object literals) are expected.

Does anyone know what in means 'triple dots', class 'ellipsis , I did some "research" but have no idea & I need more information hi Janusz, beside the ellipsis you can use each other object name like str,  Ellipsis is an object that can appear in slice notation. For example: myList[1:2, , 0] Its interpretation is purely up to whatever implements the __getitem__ function and sees Ellipsis objects there, but its main (and intended) use is in the numpy third-party library, which adds a

What does the Ellipsis object do? - Article, While idly surfing the namespace I noticed an odd looking object called Ellipsis, it does not seem to be or do anything special, but it's a globally available builtin. son interprétation est purement jusqu'à tout ce qui met en œuvre la __getitem__ fonction et voit Ellipsis objets, mais son utilisation principale (et prévue) est dans le Python numérique extension, qui ajoute un type de tableau multidimensionnel. Puisqu'il y a plus d'une dimension, le tranchage devient plus complexe qu'un simple index de

2.1.7.8 The Ellipsis Object, This object is used by extended slice notation (see the Python Reference Manual​). It supports no special operations. There is exactly one ellipsis object, named  The Object Selection By Path Only preference determines whether you can select a filled object by clicking anywhere within the object’s area with the Selection or Direct Selection tools, or whether you must click a path segment or anchor point with these tools.

Comments
  • See the answers to stackoverflow.com/questions/752602/…
  • I found it like this: I entered x=[];x.append(x);print(x), to see how it handled stringifying cyclical objects. It returned [[...]]. I thought "I wonder what happens if I type in [[...]]? My guess was it would throw a syntax error. Instead, it returned [[Ellipsis]]. Python is so weird. The Google search that ensued brought me to this page.
  • note that the ... in a recursive repr is just a placeholder and has no relation to Ellipsis
  • On a totally side note, triple dot in import means "import from two packages up".
  • @croq stackoverflow.com/q/32395926/2988730. stackoverflow.com/q/1054271/2988730. Those two should explain everything, with proper links to docs and PEP in the answers.
  • Bah humbug. You're using Ellipsis wrong. Clearly you're supposed to use it like this: a[Ellipsis,0], none of this silly ....
  • it's also used in PEP484 type hinting in stub files
  • Just in case anyone's curious: it's also used in the standard-library typing module: e.g. Callable[..., int] to indicate a callable that returns an int without specifying the signature, or Tuple[str, ...] to indicate a variable-length homogeneous tuple of strings.
  • FYI, the FastAPI framework (which is for python 3.6+) also (now) uses it. fastapi.tiangolo.com/tutorial/query-params-str-validations
  • @ArtOfWarfare you're totally right, and this is coming from someone who verbally says "ellipsis" instead of trailing off between sentences.
  • In a half-convention, I often see ... used where people want to indicate something they intend to fill in later (a 'todo' empty block) and pass to mean an block intended to have no code.
  • Python also has the NotImplemented literal, which is useful when you want your incomplete function to return something meaningful (instead of None as in your example). (Another usecase: Implementing arithmetic operations)