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This article will explain in detail what ChainMap means in python. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

Concept

1. ChainMap adds Python3.3 to collections as a convenient tool scope and environment for management.

You can combine multiple dictionaries with other mappings so that they are logically displayed and represented as a whole. It creates a single updatable view that works similar to a regular dictionary, but with some internal differences.

2. ChainMap does not merge its mappings. Instead, they are saved in the internal mapping list.

ChainMap reimplements common dictionary operations at the top of the list. Because the internal list holds references to the original input mappings, any changes in these mappings affect the entire chainMap object.

Stores the input mapping in the list, allowing you to have duplicate keys in a given chain map. If you look for the execution key, ChainMap searches the mapping list until you find the first target key. If the key is lost, you will get one as usual.

Storing mappings in a list will really work when you need to manage nested scopes, and each mapping represents a specific scope or context.

To better understand the meaning of functional domains and contexts, consider how Python parses names. When Python searches for a name, it searches in locals (), globals (), and then builtins until the first target name is found. If the name doesn't exist, you'll get a NameError. Dealing with scope and context is the most common problem you can solve.

When using ChainMap, you can link multiple dictionaries with disjoint or intersecting keys.

First of all, ChainMap allows you to treat all dictionaries as one. So you can access key-value pairs as if you were using a single dictionary. In the second case, in addition to managing the dictionary, you can use the internal mapping list to define some kind of access priority for the duplicate keys in the dictionary. Therefore, the ChainMap object is well suited for dealing with multiple contexts.

ChainMap is a strange behavior, it is a mutation, such as update, add, delete, clear, and pop-up keys, it only acts on the first mapping in the internal mapping list.

The main functions of ChainMap are:

Build updatable views from multiple input mappings.

Provides an interface similar to that of a dictionary, but with some additional features.

Input mappings are not merged, but are saved in the internal public list.

View the external changes in the input mapping.

Can contain duplicate keys with different values.

Search the internal mapping list search keys in order.

KeyErrror throws a when a key is missing after searching the entire mapping list.

Only the first mapping in the internal list is changed.

This is the end of the article on "what is the meaning of ChainMap in python". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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