Undeclared representation: How to solve Python's variable not declared error?

Python is an interpreted language. In the process of writing code, variable declaration is not necessary. However, when an undeclared variable reference is encountered during program execution, a variable undeclared error, known as "NameError", is thrown.

This kind of error generally occurs in the following situations:

1. Variable name is spelled incorrectly
   If a non-existent variable name is referenced, Python will throw a NameError . Therefore, double-check that you spell correctly when using variables.
2. Variable is not assigned a value
   Variable is not declared and variable is not assigned a value are two different concepts. A variable may have been declared but not assigned a value before use, in which case a NameError will also be thrown.
3. Variable scope error
   In Python, the scope of variables is divided into global scope and local scope. If you use an undeclared variable inside a function, Python creates a new local variable inside the function instead of using a global variable. At this time, if this variable is used outside the function, a NameError error will be thrown.

There are usually several ways to solve these errors:

1. Check variable spelling
   Check whether the variable name is spelled correctly, especially when using long variable names.
2. Make sure the variable is assigned a value
   Before using the variable, make sure the variable is assigned a value correctly. If the variable is used inside a function, you can avoid this situation by using function parameters or declaring a local variable inside the function.
3. Confirm the scope of the variable
   If you use a global variable inside a function, use the "global" keyword to declare the variable. If you use a local variable, you need to declare the variable inside the function.
4. Initialize the variable
   Initialize the variable at the beginning of the program, or before the variable is used for the first time, to ensure that it has a default value.

In summary, variable undeclared error is one of the common errors in Python, but it can be easily solved by carefully checking the code and using the correct variable scope.

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