Variables

What is a Variable?

• In programming, a variable is a container for storing data. Unlike algebraic variables, which represent unknown values, programming variables hold actual data that can be changed during program execution.

Memory and Variables

• Human Memory: Helps us retain new skills, remember the past, and plan for the future.
• Computer Memory: Functions similarly by storing and updating data. For example, a game like Super Mario keeps track of variables like time, score, level, etc.

Creating Variables

• Variable Creation: Variables are created by assigning a value to a name using the assignment operator (=).

  x = 22
  • Explanation: x is assigned the value 22.

• Syntax: Variable names are on the left side of the =, while the value is on the right.

• Unlike other languages (like JavaScript, which uses let or const to declare a variable), Python does not need explicit variable declarations.

Using Variables

• You can call or access a variable’s value by referring to its name:

  print(x)  # Output: 22
• Memory Analogy: Python searches the memory for the variable (box) labeled x, retrieves the value 22, and returns it.

Naming Variables

• Snake Case: Separate words with underscores.

  player_name = "Alex"

• Use Descriptive Names: Avoid vague names like x, y, z. Instead, use names that describe the data they hold.

  age = 22
  score = 1100

Variable Reassignment

• Reassignment: Variables can be reassigned with new values at any time.

  x = 22
  x = 1.5

Real-World Examples of Reassignment

• Example 1: Score updates in a game (e.g., Super Mario):

  score = 1100
  score = score + 100  # After earning coins

• Example 2: Updating a sports player's team:

  lebron_james_team = "Cavaliers"
  lebron_james_team = "Lakers"  # Reassigned in 2018

Data Types

What is a Data Type?

• Data Type: A classification that specifies which type of value a variable can hold.
  • Example: The variable age can hold integer values like 25, but not text values like "twenty-five".
  • Common Data Types: int, float, str, bool, list, tuple, dict.
  • Dynamic Typing: Python automatically assigns data types based on the value assigned to a variable.
  • Type Checking: You can check the data type of a variable using the type() function.

Common Data Types

Printing and String Formatting

Using print()

• The print() function is used to output messages or variable values to the screen.

  print("Game is loading...")

Combining Strings and Variables

• String Concatenation:

  username = "Alex"
  print("Welcome " + username)  # Output: Welcome Alex

f-Strings

• f-Strings provide a cleaner way to format strings, allowing variables to be embedded directly within curly braces {}:

  name = "Bob"
  score = 1100
  print(f"{name}'s score: {score}")  # Output: Bob's score: 1100

User Input

Using input()

• The input() function allows you to capture input from the user. It always returns the input as a string.

  response = input("How are you? ")
  print("You said:", response)

Type Conversion (Casting)

• Since input() returns strings, you need to convert the input to the appropriate data type when performing calculations:

  height = input("Enter your height in inches: ")
  height = int(height)  # Convert string to integer

Example: Simple Calculation Program

• A program to calculate snowboard length based on height:

  height = input("Enter your height in inches: ")
  height = int(height)
  snowboard_length = height * 2.54 * 0.88
  print(f"Your recommended snowboard length is {snowboard_length} cm.")

Conditionals

• Conditional statements allow you to control the flow of your program based on boolean expressions.

  if temperature > 75:
      print("It's hot outside!")

• If-Else: Executes one block of code if the condition is true and another if it is false.

  if temperature > 75:
      print("It's hot!")
  else:
      print("It's cool!")

• Elif is used for multiple conditions.

  if temperature > 75:
      print("It's hot!")
  elif temperature < 60:
      print("It's cold!")
  else:
      print("It's mild.")

Loops

Loops allow you to repeatedly execute a block of code as long as a condition is met. Python supports two types of loops: for loops and while loops.

For Loops

• For loops are used for iterating over a sequence (like a list, tuple, string, or range).

• Syntax:

  for variable in sequence:
      # code block

• Example 1: Iterating over a list:

  fruits = ["apple", "banana", "cherry"]
  for fruit in fruits:
      print(fruit)
  # Output: apple, banana, cherry

• Example 2: Using range() in a for loop:

  for i in range(5):
      print(i)
  # Output: 0, 1, 2, 3, 4

• Example 3: Using enumerate() in a for loop:

  for index, fruit in enumerate(fruits):
      print(i, fruit)
  # Output: 0 apple, 1 banana, 2 cherry

While Loops

• While loops repeatedly execute a block of code as long as the condition is True.
• Syntax:

  while condition:
      # code block

Break and Continue

• break: Used to exit a loop prematurely.

  • Example:

  for i in range(10):
      if i == 5:
          break
      print(i)
  # Output: 0, 1, 2, 3, 4

• continue: Skips the rest of the code inside the loop for the current iteration and moves to the next iteration.

  • Example:

  for i in range(5):
      if i == 2:
          continue
      print(i)
  # Output: 0, 1, 3, 4

Iterating Over Dictionaries

• You can loop through dictionaries using .items() to get both the key and value.
  • Example:

  dictionary = {"name": "Alex", "age": 25}
  for key, value in dictionary.items():
      print(key, value)
  # Output: name Alex, age 25

Boolean Logic and Operators

Boolean Expressions

• Boolean Values: True or False.

  is_sunny = True
  is_raining = False

Comparison Operators

• Used to compare values. Returns True or False.

  Operator	Meaning	Example
  ==	Equals	10 == 10
  !=	Not Equals	5 != 4
  >	Greater Than	7 > 3
  <	Less Than	3 < 7
  >=	Greater or Equal	5 >= 5
  <=	Less or Equal	4 <= 6

Logical Operators

• and, or, and not combine boolean expressions.

  if temperature > 75 and not raining:
      print("It's a great day!")

Functions

What is a Function?

• A function is a reusable block of code that performs a specific task.

  def greet(name):
      print(f"Hello, {name}!")

Calling a Function

• To call a function, use its name followed by parentheses and pass any required arguments:

  greet("Alice")  # Output: Hello, Alice!

Parameters and Return Values

• Functions can accept parameters and return values.

  def area(width, height):
      return width * height
   
  print(area(4, 5))  # Output: 20

Built in functions