In Python, variables are used to store values that can be accessed and manipulated within a program. However, the scope of a variable can differ depending on whether it is a global variable or a local variable. Global variables can be accessed from any part of the program, while local variables are limited to the function or block in which they are defined. Understanding the differences between variable scopes is important for developing efficient and effective Python code.
Scope of global variables in Python
Global variables are the variables that are defined outside of any function in a program. They can be accessed and modified by any function or module in the program.
The scope of a variable in Python defines its accessibility. There are two types of scopes in Python: Global scope and Local scope. A global scope means that a variable is accessible throughout the program, while a local scope means that a variable is accessible only within the function where it is defined.
In Python, global variables can be accessed and modified from any function or module in the program. However, assigning a value to a global variable inside a function creates a new local variable within that function.
Here are some examples of how the scope of global variables works in Python:
Example 1: Accessing a global variable inside a function
x = 5 #global variable def func(): print(x) #accessing a global variable inside a function func() #calling the function # Output: 5
In this example, the function
func is accessing the global variable
x which is defined outside of any function.
Example 2: Accessing the global variable outside the function
x = 5 #global variable def func(): x = 10 #creating a new local variable print(x) #accessing the local variable inside the function func() print(x) #accessing the global variable outside the function # Output: 10 5
In this example, the function
func is creating a new local variable
x by assigning it a value of
10. So, the
How global variables work in Python
Global variables are variables that can be accessed and modified throughout the code, regardless of where they are declared. The variable scopes in Python determine the accessibility of variables in different parts of the code. Python supports three variable scopes - local, global, and nonlocal. Local variables are variables that are declared and used within a particular function or block of code, and their scope is limited to that particular function or block of code.
Global variable example
# declaring and initializing a global variable global_var = "I am a global variable." def func(): # accessing and modifying the global variable within the function global global_var global_var = "I have been modified." # calling the function to modify the global variable func() # printing the modified value of the global variable print(global_var) # Output: "I have been modified."
In the above code, a global variable named
global_var is declared and initialized outside the function. The
func() function accesses and modifies the value of
global_var using the
global keyword. Finally, the modified value of the global variable is printed.
Local Variable Example
def func(): # declaring and initializing a local variable local_var = "I am a local variable." print(local_var) # calling the function that uses the local variable func() # trying to access the local variable outside the function # Output: NameError: name 'local_var' is not defined # print(local_var)
In the above code,
local_var is a local variable declared and initialized within the
func() function. The scope of this variable is limited to the function only. When the function is called, the value of
local_var is printed. However, when we try to access this variable outside the function, we get a
NameError as the variable is not defined in that scope.
The role of non-local variables in Python
Global variables are variables that can be accessed and modified from anywhere in the program, whereas local variables are only accessible within a specific function or block of code. The scope of a variable refers to the area in which it can be accessed.
Non-local variables in Python are variables that are defined in an outer function but can be accessed in an inner function. The
nonlocal keyword is used to declare a non-local variable in Python.
count = 0 # global variable def increment(): global count count += 1 print(count) increment() # output: 1 increment() # output: 2
In this example,
count is a global variable that can be accessed and modified from anywhere in the program. The
global keyword is used inside the
increment function to indicate that we are modifying the global variable
def outer(): x = "local" # local variable def inner(): nonlocal x # non-local variable x = "nonlocal" print("inner:", x) inner() print("outer:", x) outer() # output: inner: nonlocal, outer: nonlocal
In this example,
x is a local variable in the
outer function. The
inner function has access to this variable using the
nonlocal keyword, so we can modify its value. When we call the
outer function, the
inner function is executed and the value of
x is changed to
nonlocal. This change is reflected in the
outer function when we
x after the
inner function is executed.
Best practices for using global variables in function
Global variables are variables that can be accessed and modified from any part of the program. In Python, a variable's scope determines where it can be accessed. The best practice for using global variables in Python is to minimize their usage, as too many global variables can make the program difficult to understand, debug, and maintain.
One example of a global variable is the power function in Python. We can use a loop to calculate the power of a number. Here is an example:
power = 1 def calculate_power(num, exponent): global power power = 1 for i in range(exponent): power *= num return power print("Power of 2^3 is", calculate_power(2, 3)) print("Power of 5^4 is", calculate_power(5, 4))
In this example, we declare a global variable
power outside the function
calculate_power(). Inside the function, we use this global variable to store the power of the number. We reset the value of the
power variable to 1 for each new calculation.
Program to count the number of times a function is called
count = 0 def my_function(): global count count += 1 print("This function has been called", count, "times.") my_function() my_function() my_function()
In this example, we declare the global variable
count outside the function
my_function(). Inside the function, we increment the value of the
count variable every time the function is called. We then print the value of
Overall, it is generally best to avoid global variables in favor of local variables with more limited scope. However, in some cases, global variables may be necessary or useful, and we can use them carefully with the
global keyword to access them inside functions.
Advanced tips for Python variable scopes and naming conventions
Advanced tips for Python variable scopes include avoiding global variables as much as possible to prevent naming conflicts and unexpected behavior. It is also recommended to use descriptive variable names that follow the PEP 8 naming conventions, such as using lowercase letters and underscores to separate words.
Function naming conventions in Python follow the same PEP 8 guidelines, using lowercase letters and underscores to separate words. Function names should also be descriptive and convey the purpose of the function.
# Local variable def greet(name): message = "Hello, " + name + "!" return message print(greet("Alice")) # Output: Hello, Alice!
In this example, we declare a local variable
message inside the
greet() function. This variable is only accessible within the function and cannot be accessed from outside. The function takes a
name parameter and returns a greeting message with the name included.