1. Basic Introduction

1.1 What is extend?

The extend method is a widely used term in many programming languages, typically referring to a method that extends or increases the number of elements in a collection such as objects, arrays, or lists. While the specific implementation and behavior may vary across languages, the core concept remains similar. Below is an introduction and usage example of the extend method in several common programming languages.

In Python, extend is a method of the list type, used to append all elements from an iterabel (e.g., list, tuple, set) to the end of the list.

1.2 Purpoce?

• Append all elements of an iterable to the end of a list.
• Unlike the + operator, extend modifies the original list in place, while + creates a new list.

1.3 Simple Example

# Create two lists
list1 = [1, 2, 3]
list2 = [4, 5, 6]

# Use extend to merge lists
list1.extend(list2)

# Print the merged list
print(list1)  # Output: [1, 2, 3, 4, 5, 6]

2. Usage

2.1 Practical Application

In Python, if you want to add all elements from one list (e.g., loads["data"]["list"]) into another list (res["data"]["list"]), you should use the extend method instead of append. The append method adds the entire list as a single element, whereas extend adds each element individually.

2.2 Code Example

Here's how to use the extend method:

# Assume res["data"]["list"] is already a list
# and loads is a dictionary with key "data", whose value is a dictionary containing key "list" with a list value

# Use extend to add elements from loads["data"]["list"] to res["data"]["list"]
res["data"]["list"].extend(loads["data"]["list"])

This way, res["data"]["list"] will contain all eelments from loads["data"]["list"], rather than having the latter as a single nested list element.