Global and local variables are essential concepts in Python programming. The scope of variables defines their accessibility and lifespan.
In this article, we will discuss the different types of variables and how to access them. We will also delve deeper into the differences between global and local variables and provide tips and tricks to ensure efficient coding.
Types of Variables Based on Their Scope
Python variables can be categorized into three types based on their scope: local variables, global variables, and environment variables.
Local Variables
Local variables are declared inside a function, and their accessibility is limited to the function’s scope. These variables are created when the function is called and destroyed when the function returns.
Local variables cannot be accessed outside the function. For example, let’s consider the following code:
def sum(a, b):
# declaring a local variable c
c = a + b
print(c)
In this code, the variable c is a local variable.
It can only be accessed within the sum() function.
Global Variables
Global variables are declared in a module and can be accessed from anywhere in the module. Global variables have a lifespan during the duration of the program’s execution.
They are accessible across all functions and classes inside the module. For example, let’s consider the following code:
code = 21
def global_variable():
# accessing the global variable code
print(code)
In this code, the variable code is a global variable accessible inside the function global_variable(). It will produce the output ’21’ when called.
Environment Variables
Environment variables are variables defined outside the scope of the Python program. These variables are the same for all Python files, language-independent, and can be accessed through the terminal.
Some examples of environment variables are PATH, PYTHONPATH, and HOME.
Accessing Global Variables
Accessing Global Variables Globally
To access a global variable globally, you only need to define it outside a function.
When the global variable is defined outside a function, it can be accessed from anywhere within the module without any issues. For example, let’s consider the following code:
code = 30
def global_variable():
# accessing the global variable code
print(code)
# accessing the global variable code globally
print(code)
This code will produce the output ’30’ when the global variable is accessed globally.
Accessing Global Variables in a Function Scope
When you need to access a global variable from within a function, you need to use the global keyword to declare it in the function’s scope.
Otherwise, Python will treat it as a local variable, and any changes made within the function will be limited to the function’s scope. For example, let’s consider the following code:
code = 25
def global_variable():
# declaring global variable code
global code
# modifying the global variable code
code = 35
# printing the modified value of the global variable code
print(code)
global_variable()
This code will produce the output ’35’ when the global variable code is modified within the function global_variable().
Dealing With Reference Before Assignment Error
When you declare a global variable inside a function and do not use the global keyword to assign it, Python will treat it as a local variable. If you try to modify a local variable before assigning it a value, Python will throw a reference before assignment error.
For example, let’s consider the following code:
def global_variable():
# access code locally without using global keyword
print(code)
# modify code locally without using global keyword
code = 10
# print modified code
print(code)
global_variable()
This code will throw an error that says, “local variable ‘code’ referenced before assignment.” You can fix this error by using the global keyword to assign the global variable.
Conclusion
Global and local variables are essential concepts in Python programming. The scope of variables defines their accessibility and lifespan.
In this article, we discussed the different types of variables and how to access them. We also delved deeper into the differences between global and local variables and provided tips and tricks to ensure efficient coding.
By understanding variables’ scope and accessing them efficiently, you can write more effective and scalable Python programs.
Importance of Knowing Global Variables and Their Manipulation
Global variables are widely used in Python programming.
They are accessible across all functions and classes inside the module, which can be very beneficial. However, global variables can cause problems if not used cautiously.
It is essential to keep the number of global variables to a minimum to avoid confusion and conflicts. Knowing how to use and manipulate global variables can be useful when working with large-scale programs.
This can be accomplished by using specific modules or implementing a shared data approach to minimize the number of global variables. Shared data approach involves creating a separate module for all shared data and importing it whenever needed.
Another common problem with global variables is their state. Global variables can be modified anywhere within a module, which can make it difficult to track their state.
To overcome this problem, you can use a functional programming approach, where data is passed around as arguments and returned as output. This approach helps to keep the state of the program clear and understandable.
Practice
The best way to get familiar with global and local variables is to practice. Below are some examples to help you understand their usage and manipulation.
Example 1: Modifying a Global Variable Locally
code = 100
def function():
# accessing the global variable code
global code
# modifying the global variable code locally
code = 200
print("Local value of code:", code)
# accessing the global variable code globally
print("Global value of code: ", code)
function()
# checking the value of code globally after modifying it locally
print("Global value of code after modification: ", code)
Output:
Global value of code: 100
Local value of code: 200
Global value of code after modification: 200
In this example, we declared a global variable ‘code’ with a value of 100. We then defined a function ‘function’ that modifies the global variable ‘code’ locally.
We used the ‘global’ keyword to tell Python that we are modifying the global variable. Finally, we printed the global values of ‘code,’ executed the function, and printed the global value of ‘code’ after modification.
Example 2: Passing a Global Variable as a Parameter
code = 100
def function(x):
# modifying the global variable code locally
x = 200
print("Local value of code:", x)
# passing a global variable code as a parameter
function(code)
# Globally checking the value of code after passing to the function
print("Global value of code:", code)
Output:
Local value of code: 200
Global value of code: 100
In this example, we declared a global variable ‘code’ with a value of 100. We defined a function ‘function’ that takes a parameter ‘x’ and modifies it locally.
We passed the global variable ‘code’ as a parameter to the function ‘function.’ Finally, we printed the local and global values of ‘code.’
Example 3: Using a Shared Data Approach
Shared data approach helps to avoid global variable abuse. Below is how to implement it.
Create a module for shared data (shared_data.py):
GPA = 3.5
NAME = "John Doe"
AGE = 25
Create two modules. First_module.py imports the shared_data.py module; the second_module.py imports the shared_data.py module.
The modules then use the shared data to perform operations. First_module.py:
import shared_data
print("Name:", shared_data.NAME)
print("GPA:", shared_data.GPA)
Second_module.py:
import shared_data
print("Age:", shared_data.AGE)
Output:
Name: John Doe
GPA: 3.5
Age: 25
In this example, we created a module called ‘shared_data.py’. The module contains some shared data (GPA, NAME, and AGE), which can be imported and used as needed.
We then imported the ‘shared_data.py’ module into ‘First_module.py’ and ‘Second_module.py’. We print the shared data of NAME and GPA in ‘First_module.py’ and AGE in ‘Second_module.py’.
Conclusion
Global and local variables are fundamental concepts in Python programming. Understanding their use and scope can help to write efficient and robust codes.
By knowing how to manipulate global variables, you can create more effective and scalable Python programs. With practice, you can master the use of global and local variables in your Python programs to make programming easy and efficient.
In summary, understanding global and local variables is vital in Python programming. Global variables are accessible across all functions and classes inside the module, and local variables are declared within a function and have limited accessibility.
Environment variables are declared outside the Python program’s scope. We have discussed ways to access global variables, including declaring them globally or locally within a function, passing them as a parameter to a function, or implementing a shared data approach.
Manipulating global variables using the global keyword or functional programming can help avoid confusion.
Practice is the key to mastering the use of global and local variables.
By understanding these concepts, you can enhance your Python programming skills and write efficient and robust codes.