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Variables and Data Types.md

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Variables in Python

Table of Contents

Variables

A variable is a name that refers to a memory location storing data. Unlike other languages, variables do not need to be declared with a specific type in python.

Variable Declaration

Variables are created by simply assigning a value to a name:

age = 25
name = "Alice"

Rules for Naming Variables:

  • Variable names must start with a letter or an underscore (_).
  • Variable names can contain letters, numbers, and underscores but they cannot start with a number.
  • Python is case-sensitive, so age and python Age are going to be treated as two different variables.
  • Avoid using reserved keywords (e.g., if, else, for) as variable names.

Data Types

Python’s basic data types include:

  1. Integer (int): Whole numbers, positive or negative, without a decimal. Integers are unbounded in Python, meaning they can be as large as memory allows.
count = 10
  1. Float (float): Numbers with decimal points. Floats can represent fractions and real numbers.
price = 19.99
  1. String (str): A sequence of characters (letters, symbols, digits, etc.). Strings are enclosed within single, double, or triple quotes.
name = "Alice"
  1. Boolean (bool): Represents True or False values, often used for conditional expressions.
is_valid = True
  1. NoneType (None): Represents the absence of a value or a null value. Commonly used as a placeholder or default value in functions.
result = None

Type Casting and Type Checking

  • Type Casting: Converting one data type to another. Python provides several functions to convert between types:
int("10")      # Converts string to integer -> 10
float("3.14")  # Converts string to float -> 3.14
str(25)        # Converts integer to string -> "25"
bool(0)        # Converts integer to boolean -> False

  • Implicit Type Conversion: Python automatically converts data types in certain operations (e.g., adding an integer and float results in a float).

  • Type Checking: Using type() to check the data type of a variable. isinstance() checks if a variable is of a particular type:

age = 25
print(type(age))               # <class 'int'>
print(isinstance(age, int))    # True

Constants and Naming Conventions

Constants

Python doesn’t have built-in constant support, but by convention, variable names in all uppercase are used to indicate constants. Typically, constants are defined at the beginning of a script or within a module:

PI = 3.14159
MAX_USERS = 100

Naming Conventions:

  • snake_case is used for variables and functions (e.g., user_name, calculate_total).
  • ALL_CAPS is used for constants (e.g., PI, MAX_USERS).
  • CamelCase is used for class names (e.g., CustomerProfile).