Why Are Global Variables Considered Harmful in Programming?

Why Global Variables Are Notoriously Evil in Programming

The question of why global variables are considered detrimental in programming, particularly in Python, has sparked numerous debates. While not exclusive to Python, global variables pose challenges that can deteriorate code quality and lead to hidden issues.

Global variables, unlike local variables, exist outside the scope of specific functions or classes, making them accessible from anywhere within the program. This unrestricted access can introduce unintended side effects that are difficult to track down and can cripple code readability.

One major concern with global variables is that they can lead to Spaghetti code, where the flow of the program becomes tangled and difficult to navigate. Since global variables can be modified from multiple places without clearly specifying how, it can become challenging to unravel the true cause and effect relationships.

Furthermore, global variables violate the principle of modularity and encapsulation, which encourages breaking down code into self-contained units. By allowing functions and classes to modify global variables directly, it undermines the idea of distinct and cohesive modules, making code more fragile and error-prone.

However, it's important to note that global constants, which represent unchangeable data accessible from anywhere, are different from global variables. Programmers often capitalize constants by convention to distinguish them from general global variables.

Despite the potential drawbacks, there are scenarios where global state (a broader concept encompassing global variables) can be used judiciously. For instance, it can optimize algorithms, reduce complexity, enable caching, or facilitate code portability from imperative environments.

To mitigate the risks associated with global variables, it's recommended to minimize their use and favor explicit passing of data through function parameters instead. By limiting the scope of variables, code becomes more transparent, maintainable, and less susceptible to unexpected side effects.

For further exploration of this topic and the underlying concepts of side effects, it's highly recommended to delve into the principles of Functional Programming. Resources such as the provided links can provide valuable insights into these topics.

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