Primary Scope of variables (Local vs Global)

In Python, variables can have different scopes, and the two primary scopes are local and global. The scope of a variable determines where in the code it can be accessed or modified. Here's an explanation of local and global variables in Python:

1. Local Variables:

   • A variable declared inside a function is known as a local variable.

   • It is only accessible within the function where it is defined.

   • Once the function execution is complete, the local variable is destroyed, and its value is no longer accessible.

     def my_function():
         local_variable = 10
         print(local_variable)
     
     my_function()  # Output: 10
     
     # Attempting to access the local variable outside the function would result in an error
     # print(local_variable)  # This would raise an error
     

2. Global Variables:

   • A variable declared outside of any function or block is considered a global variable.

   • Global variables are accessible throughout the entire program, including inside functions.

   • However, if a function tries to modify the value of a global variable, it needs to use the global keyword.

     global_variable = 20
     
     def my_function():
         # Accessing the global variable
         print(global_variable)
     
     my_function()  # Output: 20
     
     def modify_global():
         global global_variable
         global_variable = 30
     
     modify_global()
     print(global_variable)  # Output: 30
     

3. Scope Hierarchy:

   • When both local and global variables have the same name, the local variable takes precedence within its scope.

   • If a variable is not found in the local scope, Python looks for it in the enclosing (non-local) scopes, including the global scope.

     x = 50  # Global variable
     
     def my_function():
         x = 10  # Local variable with the same name as the global variable
         print(x)
     
     my_function()  # Output: 10
     print(x)       # Output: 50 (global variable)
     

In the example above, the print(x) statement inside my_function refers to the local variable x, while the print(x) statement outside the function refers to the global variable x.

Understanding the scope of variables is crucial for writing maintainable and bug-free code. It helps prevent unintended side effects and ensures that variables are used appropriately within their intended contexts.