What does global do in Python?

What is Global in Python?

Global Variables in Python

In Python, a global variable is a variable that is defined outside of any function or class, and it can be accessed and modified from any part of the program. In this article, we will explore what global variables are, how to declare them, and some important things to keep in mind when using global variables in Python.

What are Global Variables?

In Python, a global variable is a variable that is defined outside of any function or class. It is declared using the global keyword before the variable name. Global variables are shared across all functions and classes in a program, and they can be accessed and modified from any part of the program.

Declaring Global Variables

To declare a global variable in Python, you simply assign a value to it using the = operator. Here is an example:

# Define a global variable

global my_global_variable



# Assign a value to the global variable

my_global_variable = 10



# Print the value of the global variable

print(my_global_variable)

In this example, my_global_variable is a global variable that is defined outside of any function. It is assigned a value of 10, and then printed.

Importing Global Variables

Python also allows you to import global variables from other modules. Here is an example:

# Import the global variable from another module

import my_module



# Assign a value to the imported global variable

my_module.my_global_variable = 20



# Print the value of the imported global variable

print(my_module.my_global_variable)

In this example, the global variable my_global_variable is imported from the my_module module. It is assigned a value of 20, and then printed.

Global Variables in Classes

In Python, a global variable is also accessible from any part of a class. Here is an example:

# Define a class with a global variable

class MyClass:

    _my_global_variable = 10



    def __init__(self):

        self._my_global_variable = 20



    def print_global_variable(self):

        print(self._my_global_variable)



obj = MyClass()

obj.print_global_variable()

In this example, the global variable my_global_variable is defined within the MyClass class. It is accessible from the __init__ method and the print_global_variable method.

Differences between Global and Built-in Variables

Here is a table highlighting the differences between global variables and built-in variables in Python:	Variable	Global Variable	Built-in Variable
Scope	Shared across all functions and classes	Has its own scope, within the calling function or class
Access	Can be accessed from any part of the program	Can only be accessed within the same function or class
Assignment	Assign a value using the = operator	Assign a value using the = operator, but can also be assigned using the self parameter
Imports	Can be imported from other modules	Does not have imports, as it is a built-in variable
Local	Part of the local scope	Part of the global scope, shared across all functions and classes

Importing Specific Global Variables

You can also import specific global variables from other modules, just like you would import built-in variables. Here is an example:

# Import the specific global variable from another module

import my_module



# Assign a value to the imported global variable

my_module.my_global_variable = 30



# Print the value of the imported global variable

print(my_module.my_global_variable)

In this example, the global variable my_global_variable is imported from the my_module module and assigned a value of 30. It is then printed.

Conclusion

In conclusion, global variables are an essential part of programming in Python. They allow you to share data across functions and classes, and they can be accessed and modified from any part of the program. While built-in variables have their own scope and access restrictions, global variables have their own scope and access restrictions as well. Understanding how to declare, assign, and import global variables is crucial for writing efficient and effective Python programs.

Important Tips

• Use the global keyword to declare global variables, and avoid using it unnecessarily.
• Use imports from other modules to access global variables, and be careful not to import them again if you are not sure if they are the same as the variable you are trying to access.
• Use specific variable names instead of using self as a parameter to access global variables.
• Be careful not to use global variables in static methods, as this can lead to unexpected behavior.

Best Practices

• Avoid using global variables if possible, and instead use built-in variables or other forms of sharing data.
• Use imports from other modules to access global variables, and be careful not to import them again if you are not sure if they are the same as the variable you are trying to access.
• Use specific variable names instead of using self as a parameter to access global variables.
• Keep global variables simple and obvious, and avoid making them complex or nested.