What are global variables in nested functions?

Global variables in nested functions are variables declared outside of any function, or explicitly declared as global using the global keyword within a nested function, allowing modification of the variable's value to be reflected outside the local scope of the nested function.

Understanding Variable Scope in Nested Functions

When dealing with nested functions, it's crucial to understand variable scope. A nested function is a function defined inside another function. Variables have different scopes depending on where they are defined:

• Local Scope: Variables defined within a function. They are only accessible within that function.
• Enclosing Scope: Variables defined in the enclosing function (the function containing the nested function). The nested function can access these variables.
• Global Scope: Variables defined outside of all functions. They are accessible from anywhere in the code.

How Global Variables Behave in Nested Functions

By default, if a nested function tries to assign a value to a variable that exists in the global scope, Python will create a new local variable with the same name within the nested function's scope. To explicitly modify a global variable from within a nested function, you must use the global keyword.

Using the global Keyword

The global keyword indicates that you are referring to a variable in the global scope, not creating a new local variable.

Example:

global_var = 10

def outer_function():
    def inner_function():
        global global_var  # Declare that we're using the global variable
        global_var = 20    # Modify the global variable

    inner_function()
    print("Value of global_var inside outer_function:", global_var) # Output: 20

outer_function()
print("Value of global_var outside outer_function:", global_var) # Output: 20

In this example, the global keyword within inner_function ensures that the global_var being modified is the one in the global scope. Consequently, changes made to global_var inside inner_function are reflected everywhere. According to the reference, when you change a global keyword variable inside the nested function, it will reflect outside the local scope.

Practical Implications and Considerations

• Code Clarity: Using global variables excessively can make code harder to understand and debug. It's generally recommended to minimize their use.
• Side Effects: Modifying global variables from within functions can lead to unexpected side effects, making it harder to reason about the program's behavior.
• Alternatives: Consider using function arguments and return values to pass data between functions, promoting better code organization and maintainability.

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