What are global variables inside functions?

Global variables inside functions are variables defined outside of the function's scope that can be accessed and modified within the function, but only if explicitly declared using the global keyword.

In essence, without the global keyword, a function will treat a variable with the same name as a global variable as a local variable.

Understanding Global Variables in Functions

Here's a breakdown:

Scope: Global variables exist outside any function and are accessible from anywhere in the code.
Accessibility within functions: By default, functions don't have direct access to global variables for modification.
The global keyword: To allow a function to modify a global variable, you must declare it using the global keyword inside the function. According to the reference provided on 27-Sept-2011, "Global variables are not available in a function, unless you mark which variable should be a global. Use the keyword global with a space in front of your variable name at the beginning of your function."

How to Use Global Variables Inside Functions

Here’s a step-by-step guide with an example:

Define the Global Variable: Create a variable outside any function.
```
global_variable = 10
```

Use the global Keyword Inside the Function: If you intend to modify the global variable, declare it as global within the function.

def modify_global():
    global global_variable  # Declare that we're using the global variable
    global_variable = 20   # Modify the global variable

Access/Modify (if declared global) the Variable: You can now access and/or modify the global variable within the function. If you only need to read the variable, you do not need the global keyword.
```
def print_global():
    print(global_variable) # Accessing global variable without modifying
```

Example: Modifying a Global Variable

global_variable = 10

def modify_global():
    global global_variable
    global_variable = 20
    print("Inside function:", global_variable)

def print_global():
    print("Outside function before modification:", global_variable)

print_global() # Output: Outside function before modification: 10
modify_global() # Output: Inside function: 20
print_global() # Output: Outside function after modification: 20

In this example, the modify_global function uses the global keyword to indicate that it's working with the global variable. The change made inside the function affects the global variable's value, which is then reflected when print_global is called again.

Practical Insights

Avoid Overuse: Excessive use of global variables can make code harder to understand and maintain. Consider alternative approaches like passing variables as arguments or using object-oriented programming techniques.
Naming Conventions: Using clear and distinct names for global variables helps in avoiding naming conflicts and improves code readability.
Scope Awareness: Always be mindful of the scope of your variables to prevent unintended side effects.