Add Python beginner examples with heavily-commented code

01_variables.py

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+#!/usr/bin/env python3
+"""
+01_variables.py
+
+This file demonstrates the four basic data types in Python:
+- int (integers/whole numbers)
+- float (floating-point/decimal numbers)
+- string (text)
+- bool (boolean - True or False)
+
+Variables are like containers that store information.
+You can create a variable by giving it a name and assigning it a value using =
+"""
+
+# ============================================================================
+# INTEGER (int) - Whole numbers without decimal points
+# ============================================================================
+
+# Create an integer variable called 'age'
+age = 25
+print("Age:", age)  # Output: Age: 25
+print("Type of age:", type(age))  # type() tells us what kind of data it is
+
+# Integers can be positive, negative, or zero
+score = 100
+temperature = -5
+zero = 0
+
+print("\nInteger examples:")
+print("Score:", score)
+print("Temperature:", temperature)
+print("Zero:", zero)
+
+# You can do math with integers
+sum_result = 10 + 5  # Addition
+difference = 10 - 3  # Subtraction
+product = 4 * 7      # Multiplication
+quotient = 20 // 4   # Integer division (gives whole number result)
+
+print("\nMath with integers:")
+print("10 + 5 =", sum_result)
+print("10 - 3 =", difference)
+print("4 * 7 =", product)
+print("20 // 4 =", quotient)
+
+
+# ============================================================================
+# FLOAT (float) - Numbers with decimal points
+# ============================================================================
+
+# Create a float variable called 'pi'
+pi = 3.14159
+print("\n\nPi:", pi)
+print("Type of pi:", type(pi))
+
+# Floats are used when you need precision with decimals
+height = 5.9     # Height in feet
+price = 19.99    # Price in dollars
+temperature_celsius = 36.6  # Body temperature
+
+print("\nFloat examples:")
+print("Height:", height, "feet")
+print("Price: $", price)
+print("Temperature:", temperature_celsius, "°C")
+
+# Math with floats
+result1 = 10.5 + 2.3  # Addition with floats
+result2 = 7.5 - 1.2   # Subtraction with floats
+result3 = 3.0 * 2.5   # Multiplication with floats
+result4 = 9.0 / 2.0   # Division with floats (always gives float result)
+
+print("\nMath with floats:")
+print("10.5 + 2.3 =", result1)
+print("7.5 - 1.2 =", result2)
+print("3.0 * 2.5 =", result3)
+print("9.0 / 2.0 =", result4)
+
+
+# ============================================================================
+# STRING (str) - Text data enclosed in quotes
+# ============================================================================
+
+# Create a string variable called 'name'
+# You can use single quotes ' ' or double quotes " "
+name = "Alice"
+print("\n\nName:", name)
+print("Type of name:", type(name))
+
+# Strings can contain letters, numbers, spaces, and special characters
+greeting = "Hello, World!"
+address = '123 Main Street'
+message = "I am learning Python!"
+
+print("\nString examples:")
+print(greeting)
+print("Address:", address)
+print(message)
+
+# You can combine (concatenate) strings with +
+first_name = "John"
+last_name = "Doe"
+full_name = first_name + " " + last_name  # Notice the space in the middle
+print("\nCombining strings:")
+print("Full name:", full_name)
+
+# You can repeat strings with *
+laugh = "Ha" * 3  # Repeats "Ha" three times
+print("Laugh:", laugh)  # Output: HaHaHa
+
+# Strings have many useful methods (functions that work on strings)
+sentence = "python is awesome"
+print("\nString methods:")
+print("Original:", sentence)
+print("Uppercase:", sentence.upper())  # Converts to UPPERCASE
+print("Capitalized:", sentence.capitalize())  # Capitalizes first letter
+print("Length:", len(sentence))  # len() gives the number of characters
+
+
+# ============================================================================
+# BOOLEAN (bool) - True or False values
+# ============================================================================
+
+# Create boolean variables
+is_student = True
+is_raining = False
+print("\n\nIs student:", is_student)
+print("Is raining:", is_raining)
+print("Type of is_student:", type(is_student))
+
+# Booleans are often the result of comparisons
+is_greater = 10 > 5   # Is 10 greater than 5? True
+is_equal = 7 == 7     # Is 7 equal to 7? True
+is_less = 3 < 2       # Is 3 less than 2? False
+
+print("\nBoolean comparisons:")
+print("10 > 5:", is_greater)
+print("7 == 7:", is_equal)
+print("3 < 2:", is_less)
+
+# More comparison operators:
+print("\nMore comparisons:")
+print("5 != 3:", 5 != 3)    # != means "not equal to"
+print("8 >= 8:", 8 >= 8)    # >= means "greater than or equal to"
+print("4 <= 2:", 4 <= 2)    # <= means "less than or equal to"
+
+# You can use logical operators: and, or, not
+has_ticket = True
+has_id = True
+can_enter = has_ticket and has_id  # Both must be True
+
+print("\nLogical operators:")
+print("Has ticket:", has_ticket)
+print("Has ID:", has_id)
+print("Can enter (needs both):", can_enter)
+
+is_weekend = False
+is_holiday = True
+can_sleep_in = is_weekend or is_holiday  # At least one must be True
+
+print("Is weekend:", is_weekend)
+print("Is holiday:", is_holiday)
+print("Can sleep in (needs one):", can_sleep_in)
+
+is_awake = False
+is_asleep = not is_awake  # not flips True to False and vice versa
+
+print("Is awake:", is_awake)
+print("Is asleep (opposite of awake):", is_asleep)
+
+
+# ============================================================================
+# VARIABLE NAMING RULES AND BEST PRACTICES
+# ============================================================================
+
+print("\n\n=== Variable Naming Tips ===")
+print("✓ Use descriptive names: 'student_age' instead of 'x'")
+print("✓ Use lowercase with underscores: 'first_name' not 'firstName'")
+print("✓ Start with letter or underscore: 'name' or '_value'")
+print("✗ Don't start with numbers: '1name' is invalid")
+print("✗ Don't use Python keywords: 'if', 'for', 'while', etc.")
+print("✗ Don't use spaces: 'my name' is invalid, use 'my_name'")
+
+
+# ============================================================================
+# SUMMARY
+# ============================================================================
+
+print("\n\n=== SUMMARY ===")
+print("int: Whole numbers (no decimals)")
+print("float: Numbers with decimals")
+print("string: Text enclosed in quotes")
+print("bool: True or False values")
+print("\nYou can check any variable's type using type(variable_name)")
+print("Variables can be reassigned to new values at any time!")