


What is the purpose of the Ellipsis object (...) in Python?
Jun 09, 2025 am 12:09 AMEllipsis (...) in Python has three main uses: 1. As a placeholder for code stubs or unfinished logic, such as temporarily leaving a blank structure in a function or class; 2. Indicate all leading dimensions in multi-dimensional array slices (such as NumPy), simplifying access to high-dimensional data; 3. In Python 3.9 type prompts to represent mutable or unspecified parameters, such as in combination with typing.Concatenate. These uses correspond to structural reservations, simplified high-dimensional data slicing and complex type declarations in the early stages of development. Although they are not commonly used, they are very practical in specific scenarios.
In Python, the Ellipsis object ( ...
) might seem like a mysterious or rarely used feature, but it does have some practical purposes, especially in specific contexts like slicing and type hinging.
1. Placeholder in Stubs and Incomplete Code
One of the most common uses for ...
is as a placeholder when writing stubs or incomplete code. It's especially handy during development when you want to define a function or class structure without implementing the logic yet.
For example:
def process_data(data): ...
This tells anyone reading the code (including future you) that this function is intentionally left blank for now. It's cleaner than using pass
sometimes, and in some IDEs or tools, it might be treated differently.
You could also use it in classes:
class MyClass: ...
This avoids syntax errors while allowing you to build out the structure first.
2. Multidimensional Array Slicing (Especially in NumPy)
Another major use case appears when working with multidimensional arrays — particularly in libraries like NumPy.
Here's how it looks:
import numpy as np arr = np.random.rand(5, 5, 5) print(arr[..., 0]) # Equivalent to arr[:, :, 0]
In this context, ...
stands for "all preceding dimensions." So instead of typing out multiple colons ( :
), you can use ...
to refer to all dimensions except the last one (or whichever comes after).
It makes your slicing more readable, especially when dealing with higher-dimensional data like images or tensors.
3. Type Hinting in Python 3.9
With the evolution of Python's type system, ...
also plays a role in type hints.
For instance, it's used in typing.Unpack
, typing.Concatenate
, and other advanced type constructs introduced in later versions of Python.
A simple example:
from typing import Callable, Concatenate def decorator(func: Callable[Concatenate[int, ...], None]) -> None: ...
Here, ...
means that the function can take any additional arguments after the int
. It helps express variable-length argument lists in a flexible way.
Summary
- Use
...
as a lightweight placeholder in functions and classes during early development. - Leverage it in array slicing to simplify access to high-dimensional data.
- Utilize it in complex type hints to represent variable or unspecified parameters.
It's not something you'll use every day, but when you need it, it fits just right.
The above is the detailed content of What is the purpose of the Ellipsis object (...) in Python?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

Polymorphism is a core concept in Python object-oriented programming, referring to "one interface, multiple implementations", allowing for unified processing of different types of objects. 1. Polymorphism is implemented through method rewriting. Subclasses can redefine parent class methods. For example, the spoke() method of Animal class has different implementations in Dog and Cat subclasses. 2. The practical uses of polymorphism include simplifying the code structure and enhancing scalability, such as calling the draw() method uniformly in the graphical drawing program, or handling the common behavior of different characters in game development. 3. Python implementation polymorphism needs to satisfy: the parent class defines a method, and the child class overrides the method, but does not require inheritance of the same parent class. As long as the object implements the same method, this is called the "duck type". 4. Things to note include the maintenance

The digital asset market attracts global attention with its high volatility. In this environment, how to steadily capture returns has become the goal pursued by countless participants. Quantitative trading, with its dependence on data and algorithm-driven characteristics, is becoming a powerful tool to deal with market challenges. Especially in 2025, this time node full of infinite possibilities is combined with the powerful programming language Python to build an automated "brick-moving" strategy, that is, to use the tiny price spreads between different trading platforms for arbitrage, which is considered a potential way to achieve efficient and stable profits.

A class method is a method defined in Python through the @classmethod decorator. Its first parameter is the class itself (cls), which is used to access or modify the class state. It can be called through a class or instance, which affects the entire class rather than a specific instance; for example, in the Person class, the show_count() method counts the number of objects created; when defining a class method, you need to use the @classmethod decorator and name the first parameter cls, such as the change_var(new_value) method to modify class variables; the class method is different from the instance method (self parameter) and static method (no automatic parameters), and is suitable for factory methods, alternative constructors, and management of class variables. Common uses include:

Golangofferssuperiorperformance,nativeconcurrencyviagoroutines,andefficientresourceusage,makingitidealforhigh-traffic,low-latencyAPIs;2.Python,whileslowerduetointerpretationandtheGIL,provideseasierdevelopment,arichecosystem,andisbettersuitedforI/O-bo

TointegrateGolangserviceswithexistingPythoninfrastructure,useRESTAPIsorgRPCforinter-servicecommunication,allowingGoandPythonappstointeractseamlesslythroughstandardizedprotocols.1.UseRESTAPIs(viaframeworkslikeGininGoandFlaskinPython)orgRPC(withProtoco

Parameters are placeholders when defining a function, while arguments are specific values ??passed in when calling. 1. Position parameters need to be passed in order, and incorrect order will lead to errors in the result; 2. Keyword parameters are specified by parameter names, which can change the order and improve readability; 3. Default parameter values ??are assigned when defined to avoid duplicate code, but variable objects should be avoided as default values; 4. args and *kwargs can handle uncertain number of parameters and are suitable for general interfaces or decorators, but should be used with caution to maintain readability.

Python's garbage collection mechanism automatically manages memory through reference counting and periodic garbage collection. Its core method is reference counting, which immediately releases memory when the number of references of an object is zero; but it cannot handle circular references, so a garbage collection module (gc) is introduced to detect and clean the loop. Garbage collection is usually triggered when the reference count decreases during program operation, the allocation and release difference exceeds the threshold, or when gc.collect() is called manually. Users can turn off automatic recycling through gc.disable(), manually execute gc.collect(), and adjust thresholds to achieve control through gc.set_threshold(). Not all objects participate in loop recycling. If objects that do not contain references are processed by reference counting, it is built-in

Iterators are objects that implement __iter__() and __next__() methods. The generator is a simplified version of iterators, which automatically implement these methods through the yield keyword. 1. The iterator returns an element every time he calls next() and throws a StopIteration exception when there are no more elements. 2. The generator uses function definition to generate data on demand, saving memory and supporting infinite sequences. 3. Use iterators when processing existing sets, use a generator when dynamically generating big data or lazy evaluation, such as loading line by line when reading large files. Note: Iterable objects such as lists are not iterators. They need to be recreated after the iterator reaches its end, and the generator can only traverse it once.
