Python global variables

In Python programming, global variables are variables that are accessible and usable throughout the entire program. Within a function, we can declare a variable as global using the global keyword, allowing us to modify the global variable within the function. This article will detail the concept, usage, and considerations of global variables in Python.

What are global variables?

Global variables are variables defined globally within a program and can be accessed and modified by any function, method, or class within the program. In Python, global variables are typically defined outside of a function. If you want to assign a value to a global variable within a function, you need to declare it using the global keyword.

Next, we’ll use example code to demonstrate the basic usage and features of global variables.

# Define a global variable
global_variable = "geek-docs.com"

# Use a global variable within a function
def print_global_variable():
print(global_variable)

# Call a function
print_global_variable()

Running the above code will output the value of the global variable geek-docs.com.

How to modify a global variable within a function?

In Python, if you want to modify a global variable within a function, you need to declare it using the global keyword. Otherwise, Python will treat any variables with the same name within the function as local variables. The following is an example code for modifying a global variable:

# Define a global variable
global_variable = "geek-docs.com"

# Modify a global variable within a function
def modify_global_variable():
global global_variable
global_variable = "www.geek-docs.com"

# Print the value of the global variable before calling the function
print("Before modifying global variable: ", global_variable)

# Call the function to modify the global variable
modify_global_variable()

# Print the modified value of the global variable after calling the function
print("After modifying global variable: ", global_variable)

Running the above code will print the values of the global variable before and after the modification.

Global Variable Precautions

When using global variables, be aware of the following:

Global variables can easily lead to naming conflicts: In large programs, global variable names may be used by multiple functions or modules, which can easily lead to naming conflicts. Therefore, it is best to avoid excessive use of global variables in large programs.
Global variables can affect code readability: Excessive use of global variables can make code less readable. It is recommended to avoid modifying global variables within functions and to use global variables appropriately.
Global variable lifecycle: The lifecycle of a global variable is related to the entire execution of the program. Therefore, it is very important to use global variables appropriately within your program.

In summary, global variables are a very useful concept in Python programming, allowing us to conveniently share data within our programs. However, to avoid potential problems, it is recommended to use global variables with caution.

Conclusion

This article detailed the concepts, usage, and considerations of global variables in Python. By studying this article, readers should have a deeper understanding of global variables in Python and be able to flexibly use them in their programs.