1.3 Variables

Variables in Python are fundamental building blocks for storing and manipulating data. They allow you to assign values, perform operations, and organize information in your programs. Understanding how to name and use variables effectively is crucial for writing clean, readable code.

Python's dynamic typing system gives you flexibility in working with different data types. By following naming conventions and avoiding reserved keywords, you can create clear, meaningful variable names that enhance your code's readability and maintainability.

Variables in Python

Assigning and printing variables

• Assign values to variables using the assignment operator = which binds a value to a variable name (x = 5 assigns the value 5 to the variable x)
• Print the value of a variable using the print() function (print(x) outputs the value of x)
• Assign values of different data types to variables including numeric types (integers like x = 10, floats like y = 3.14), string type (text enclosed in single or double quotes like name = "John"), and boolean type (is_valid = True)
• Perform operations on variables and assign the result to another variable (z = x + y assigns the sum of x and y to z)
• Python uses dynamic typing, allowing variables to change types during runtime

Python variable naming conventions

• Use lowercase letters for variable names with words separated by underscores (snake_case) to enhance readability (student_name, total_score)
• Begin variable names with a letter (a-z) or an underscore (_count, score1)
• Include letters, numbers, and underscores after the first character (x2, final_score_3)
• Remember that variable names are case-sensitive so age and Age are different variables
• Select descriptive and meaningful names for variables to clarify their purpose (student_count instead of sc)
• Avoid single-character variable names except for simple loop counters like i or j

Valid names vs reserved keywords

• Valid variable names follow the Python naming rules (score, total_marks, is_passed, _private_var)
• Reserved keywords are predefined words in Python with special meanings that cannot be used as variable names (if, else, for, while, def, class, import, return)
• Avoid naming conflicts with reserved keywords by:
  1. Using synonyms or alternative names (class_name or class_type instead of class)
  2. Adding prefixes or suffixes to the variable name (for_loop or loop_for instead of for)

Variable scope and lifetime

• Scope refers to the region of the program where a variable is accessible
• Variables can have local scope (accessible only within a function) or global scope (accessible throughout the entire program)
• Use the global keyword to modify a global variable from within a function
• Python uses namespaces to organize and manage variable names
• Garbage collection automatically frees memory occupied by variables that are no longer in use