Using global variables in a function

Python Global Variables Scope

When working with functions in Python, there may be situations where you need to create or use global variables inside a function. Global variables are variables that can be accessed anywhere within your code, including inside functions.

Creating a global variable inside a function

To create a global variable inside a function, you need to use the global keyword. The global keyword is used to indicate that the variable being defined is a global variable, rather than a local variable that is only accessible within the function.

Here's an example:

def my_function():
    global my_variable
    my_variable = 10
    
my_function()
print(my_variable)  # Output: 10

In the above example, we define a global variable my_variable inside the function my_function using the global keyword. When the function is called and executed, the value of my_variable is set to 10. We can then access and print the value of my_variable outside the function.

Using a global variable in multiple functions

If you want to use a global variable that was defined inside one function in other functions as well, you can simply use the global variable wherever you need it in those functions.

Here's an example:

def set_name():
    global name
    name = "John"

def print_name():
    print("Hello, " + name)

set_name()
print_name()  # Output: Hello, John

In this example, we have two functions: set_name and print_name. The set_name function sets the value of the global variable name to "John" using the global keyword. The print_name function then prints the value of the global variable name. By calling both functions in the correct order, we can see that the value of the global variable is accessible and can be used in multiple functions.

Global variables and local variables

It's important to understand the difference between global variables and local variables. Global variables are defined outside of any function and can be accessed and modified by any part of the code.

Local variables, on the other hand, are defined inside a specific function and can only be accessed within that function. They have a local scope, meaning they are only visible and usable within the function where they are defined.

Here's an example to illustrate the difference:

def my_function():
    global global_variable
    local_variable = 10
    global_variable = 100

my_function()
print(local_variable)    # Output: NameError: name 'local_variable' is not defined
print(global_variable)   # Output: 100

In this example, we have a global variable global_variable and a local variable local_variable. When we try to access the local_variable outside the function, we get a NameError because it is only defined and accessible within the function. However, we can access and print the value of the global variable global_variable outside the function.

Avoiding the use of global variables

While global variables can be useful in some cases, it's generally recommended to avoid using them when possible. Using global variables can make your code more difficult to understand and maintain, as they can be modified by any part of the code. It's usually better to use function parameters and return values to pass data between functions.

Instead of relying on global variables, consider the following alternatives:

  • Passing parameters to functions: Instead of using a global variable, you can pass the required data as a parameter to the function.
  • Returning values from functions: Instead of modifying a global variable inside a function, you can return the modified value from the function and assign it to a variable outside the function.
  • Using classes and objects: If you have a large amount of data that needs to be shared between functions, consider using classes and objects to encapsulate the data and methods that operate on it.

Conclusion

In conclusion, creating and using global variables inside a function in Python is possible by using the global keyword. However, it's recommended to use global variables sparingly and consider alternative approaches when possible. Understanding the difference between global variables and local variables is essential for writing clean and maintainable code.

By following the examples and guidelines provided in this article, you should now have a clear understanding of how to create and use global variables inside a function in Python.

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