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In programming, a global variable is a variable that is declared outside of any function or block of code, making it accessible and modifiable throughout the entire program. Global variables have a global scope, meaning they can be used from any part of the code, including inside functions, classes, or other blocks, for instance (code): 

Its output is:

It's important to use global variables carefully, as overuse or misuse can lead to code that is harder to understand, maintain, and debug. In many cases, it's recommended to limit the use of global variables and instead use local variables within functions or pass variables explicitly as parameters to functions. In other words, the use of global variables in Python, or any programming language, can be a topic of debate and depends on the context and specific requirements of your code. Using global variables can introduce potential issues, and some best practices suggest minimizing their use.

Some reasons why using global variables might be discouraged are below: 

1. Namespace Pollution: 

   Global variables can clutter the global namespace, making it harder to keep track of variable names and increasing the risk of naming conflicts. 

2. Code Maintainability: 

   Code becomes less modular and harder to maintain when global variables are modified from various places in the codebase. Debugging and understanding the flow of data become more challenging. 

3. Code Reusability: 

   Code with global variables may be less reusable because it depends on external variables, making it less flexible for use in different contexts. 

4. Testing and Debugging: 

   Global variables can make unit testing more difficult since functions may depend on external states that are not explicitly passed as arguments. 

However, there are situations where using global variables is appropriate or even necessary: 

1. Configuration Settings: 

   Constants or configuration settings that are unlikely to change during program execution may be stored in global variables. 

2. Singletons: 

   In some cases, global variables are used to implement singleton patterns, where there's only one instance of a class. 

3. Performance Considerations: 

   In certain performance-critical scenarios, using global variables might be more efficient than passing variables as function arguments. 

To mitigate some of the issues associated with global variables, we often consider alternative approaches such as using function arguments, encapsulating data within classes, or employing design patterns like dependency injection. 

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