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Editor to share with you the python namespaces and scope of the example analysis, I believe that most people do not understand, so share this article for your reference, I hope you will learn a lot after reading this article, let's go to understand it!

The function inside the function can only be called inside the function, not outside the function. You will know why this happens through the following study.

I. namespace

Namespaces (name spaces): in the chapter on memory management, we mentioned that the creation of variables is actually opening up a new space in memory. But we have been avoiding the storage of variable names, in fact, there is a memory space in memory to store the binding relationship between variable names and variables, and this space is called namespace, and the real place to store the name is the stack area. the namespace only divides the stack into several parts, and with the namespace, we can store the same name in the stack area.

1.1 built-in namespace

Built-in namespaces: store the names included in the Pyhton interpreter, such as int, float, len

Life cycle: takes effect when the interpreter starts and expires when the interpreter is closed

1.2 Global namespace

Global namespaces: except for built-in and local names, the rest are stored in global namespaces, such as x, func, l, z in the following code

Life cycle: takes effect when the file is executed and expires after the end of the file execution

1.3 Local namespaces

Local namespace: used to store the name generated by the function body during the function call, such as f2 in the following code

Life cycle: takes effect during the function call when the file is executed and expires after the end of the function execution

Note: even for the same function, even if it is empty, if we call it multiple times, the call produces a local namespace at a time

1.4 loading order

Because the .py file is opened by the Python interpreter, the file must not be opened until the loading of the built-in namespace in the Python interpreter finishes. Global namespaces will only be generated at this time, but local namespaces will only be generated when a function in the file is called, so the loading order of namespaces is: built-in-"global -" local.

1.5 search order

Because namespaces are used to store the binding relationship between variable names and values, whenever you want to look for names, you must find them in one of three, in the following order:

Start with the current location, and if the current location is a local namespace, the search order is: local-"global -" built-in.

II. Scope

Domain refers to the area, and the scope is the area of action.

2.1 Global scope

Global scope: globally valid, shared by all functions, including built-in and global namespaces.

2.2 Local scope

Local scope: local small, temporary storage, including only local namespaces.

2.3 pay attention

It should be noted that the scope relationship is fixed in the function definition phase and has nothing to do with the function call.

2.4 function object + scope Application

Third, supplementary knowledge point 3.1 global keyword

Modify variables in the global scope.

3.2 nonlocal keyword

Modify variables in the local scope.

3.3 pay attention

If you want to modify the global mutable type locally, you don't need any declaration, you can modify it directly.

Locally, if you want to modify the global immutable type, you need to use the global declaration to declare a global variable, which can be modified directly.

The above is all the content of the article "sample Analysis of namespaces and scopes in python". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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