Detailed explanation of the ellipsis assignment method in Python

Ellipsis assignment in Python

I did some answering questions about CSDN's Python skill tree and got involved in the usage of ‘…’, so I learned more about the relevant usage.

In Python programming, the ellipsis (...) is a special object, often called Ellipsis.

Although it is not widely used in daily programming, it is very useful in specific scenarios, especially in case of function placeholding, unimplemented method examples, and NumPy array processing.

This article will use examples toa = ...The assignment method is explained in detail.

1. Basic concepts

First, the ellipsis is a singleton object that can be used directly in the code, withNonesimilar.

For example:

a = ...
print(a)  # Output：Ellipsis

In this example, the variableaAssigned as an ellipsis object, you can see that the output result isEllipsis。

2. Use of placeholders

During development, we may need to define functions or classes, but the specific logic has not been implemented yet. At this point, we can use...As a placeholder, keeps the code structure complete.

This is very helpful for subsequent development.

def my_function():
    ...
    
class MyClass:
    def my_method(self):
        ...

In the above example,my_functionandMyClass.my_methodNone has been implemented yet, but use...Ensures the readability and maintainability of the code.

3. Indicates unimplemented methods

In API design, use...Methods that have not been implemented can be identified to alert other developers to supplement features.

For example:

class API:
    def fetch_data(self):
        ...
        
    def process_data(self):
        ...

Herefetch_dataandprocess_dataNone of the methods have been implemented yet. By using ellipsis, the developer clearly knows that these methods need subsequent supplementation.

4. Advanced Indexing in NumPy

Ellipsis is very common in NumPy libraries, especially when dealing with multidimensional arrays.

It can be used to represent all remaining dimensions, making array operations more flexible.

import numpy as np

# Create a 3D arrayarr = ([[[1, 2], [3, 4]], [[5, 6], [7, 8]]])

# Use the ellipsis to select all first elementssliced = arr[..., 0]  
print(sliced)  # Output：[[1 3] [5 7]]

In this example,slicedReturns an array containing the first element of each subarray.

use...Simplifies the code to make it more readable.

in conclusion

Although in Python,a = ...The assignment method of 'is simple, but its application scenarios are quite wide.

From placeholders to advanced indexes of NumPy arrays, ellipses provide a flexible and clear way to handle unfinished tasks and complex data structures.

Mastering this technique will help improve your Python programming skills.

The above is personal experience. I hope you can give you a reference and I hope you can support me more.