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This article is about Python global variables and local variables. Xiaobian thinks it is quite practical, so share it with everyone for reference. Let's follow Xiaobian and have a look.

Before we learn about global and local variables, let's first learn about scope.

a = 10def func(): b = 20 def inner(): c = 30

For example, print a,b,c.

You can see that only a prints 10, b and c both report errors, which is the scope problem.

We create a new.py file as a module, in the module defined variables, such as a, is the module's global variables, acting globally, no matter where you can call,

But b and c are defined inside the function, we call them local variables, and can only act inside the function.

We're looking at a problem.

Can func and inner function call variable a?

Can func call variable c?

The answer is: a is a global variable and can be called anywhere.

But func function can not call c, then we regard func as a whole, then inner is the function defined inside func, c is the variable inside inner

Summary: Variable definitions can be called anywhere globally, defined within functions, and can only be used within functions.

Variable search order: LEGB

Local scope> Outer scope> Global in current module>Python built-in scope;

There are two methods for global and local variables: global and nonlocal.

Let's go straight to the example:

We can see that if we define a locally, then we call a directly and we get an error.

The call prints only after it is defined, and the a value of the global variable does not change

What if I now wanted to change the value of a in the local namespace? At this point, we need to use global.

We can see that the value of global variable a has been modified to 15.

Here's a nonlocal:

We see an error when printing a and b at this time. The error prompt is that b is not defined.

However, a does not report an error because a is a global variable and b is a local variable, so this error occurs. The correction is as follows:

Because b is a local variable, it is declared nonlocal before calling, and then it can be called.

namespace

namespace classification

Global namespace: Created when each module is loaded and executed, it records the variables defined in the module, including functions defined in the module, classes, other imported modules, module-level variables and constants.

Local namespace: The namespace owned by each function, which records all variables defined in the function, including function parameters and internally defined local variables.

Built-in namespaces: accessible to any module, with built-in functions and exceptions (e.g. input, print, str, list, tuple...).

Load order of namespaces

Built-in namespace (load before program runs)-> global namespace (program runs: load from top to bottom)-> local namespace (program runs: load when called)

The order in which namespaces are valued

Local calls: Local namespaces 1> Global namespaces 1> Built-in namespaces

Global calls: Global namespaces I> Built-in namespaces

To sum up, when looking for variables, look for small areas, layer by layer to large areas.

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