Python Coding Worksheet Study Notes

Python is a versatile, high-level programming language known for its readability and ease of use. It is widely used in web development, data analysis, artificial intelligence, and more. For 9th graders, Python provides an excellent foundation for understanding programming concepts.

🐍 Python Basics

💡 Variables and Data Types

Variables are used to store data in a program. In Python, you don't need to declare the type of a variable explicitly; Python infers it. Common data types include:

• Integers (int): Whole numbers without a decimal point. Example: age = 15
• Floating-point numbers (float): Numbers with a decimal point. Example: price = 19.99
• Strings (str): Sequences of characters, enclosed in single or double quotes. Example: name = "Alice"
• Booleans (bool): Represents truth values: True or False. Example: is_student = True

💬 Input and Output

Programs often need to interact with the user. Python provides simple functions for this:

• print(): Displays output to the console.

  print("Hello, World!")

  name = "Bob"
print(f"My name is {name}.")

• input(): Reads input from the user as a string.

  user_name = input("Enter your name: ")
print(f"Nice to meet you, {user_name}!")

  Remember that input() always returns a string. If you need a number, you'll have to convert it using int() or float().

  num_str = input("Enter a number: ")
num_int = int(num_str)
print(f"Your number doubled is {num_int * 2}")

➕ Operators

Operators are symbols that perform operations on values and variables.

Arithmetic Operators

Operator	Description	Example
+	Addition	\(5 + 3 = 8\)
-	Subtraction	\(10 - 4 = 6\)
*	Multiplication	\(2 \times 6 = 12\)
/	Division (float)	\(7 / 2 = 3.5\)
//	Floor Division (int)	\(7 // 2 = 3\)
%	Modulo (Remainder)	\(7 % 3 = 1\)
	Exponentiation	\(2 3 = 8\)

Comparison Operators

These operators compare two values and return a Boolean (True or False).

Operator	Description	Example
==	Equal to	\(5 == 5\) is True
!=	Not equal to	\(5 != 3\) is True
>	Greater than	\(10 > 7\) is True
<	Less than	\(4 < 9\) is True
>=	Greater than or equal to	\(5 >= 5\) is True
<=	Less than or equal to	\(3 <= 2\) is False

Logical Operators

These combine conditional statements.

Operator	Description	Example
and	True if both conditions are True	(5 > 3) and (2 < 4) is True
or	True if at least one condition is True	(5 < 3) or (2 < 4) is True
not	Reverses the result; True becomes False and vice versa	not (5 > 3) is False

⚙️ Control Flow

Control flow statements determine the order in which instructions are executed.

🤔 Conditional Statements (if, elif, else)

These allow your program to make decisions based on conditions.

score = 85
if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
else:
    print("Grade: C or lower")

Remember to use indentation to define code blocks for if, elif, and else.

🔄 Loops (for, while)

Loops are used to repeat a block of code multiple times.

for Loop

Used for iterating over a sequence (like a list, string, or range of numbers).

# Loop through numbers 0 to 4
for i in range(5):
    print(i)

# Loop through items in a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

The range(n) function generates numbers from \(0\) up to (but not including) \(n\).

while Loop

Repeats a block of code as long as a condition is True.

count = 0
while count < 3:
    print(f"Count is {count}")
    count = count + 1 # or count += 1

Be careful to include a way for the condition to eventually become False, otherwise, you'll create an infinite loop!

📦 Data Structures

Data structures are ways to organize and store data.

📝 Strings

Strings are immutable sequences of characters. You can access individual characters or parts of a string.

• Indexing: Access a single character using its position (index starts at 0).

  my_string = "Python"
print(my_string[0]) # Output: P
print(my_string[5]) # Output: n

• Slicing: Extract a portion (substring) of a string.

  my_string = "Programming"
print(my_string[0:4]) # Output: Prog
print(my_string[4:]) # Output: ramming

• Length: Use len() to find the number of characters.

  len("hello") # Returns 5

📋 Lists

Lists are ordered, mutable (changeable) collections of items. They can hold items of different data types.

• Creating a List:

  my_list = [10, 20, "hello", True]

• Accessing Items: Like strings, use indexing.

  print(my_list[0]) # Output: 10

• Modifying Items:

  my_list[1] = 25
print(my_list) # Output: [10, 25, 'hello', True]

• Adding Items: Use .append() to add to the end.

  my_list.append("world")
print(my_list) # Output: [10, 25, 'hello', True, 'world']

• Removing Items: Use .remove() to remove the first occurrence of a value.

  my_list.remove(10)
print(my_list) # Output: [25, 'hello', True, 'world']

• Length: Use len().

  len(my_list) # Returns 4

🚀 Functions

Defining and Calling Functions

Functions are blocks of organized, reusable code that perform a single, related action. They help break down complex problems into smaller, manageable parts.

• Defining a Function: Use the def keyword.

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

  name is a parameter, a placeholder for data the function needs.

• Calling a Function: Use the function's name followed by parentheses, passing in arguments (actual values).

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

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

• Return Values: Functions can send back a result using the return keyword.

  
  def add_numbers(a, b):
      sum_result = a + b
      return sum_result
  
  total = add_numbers(5, 7)
  print(total) # Output: 12
          

ℹ️ Comments

Comments are lines in the code that are ignored by the Python interpreter. They are used to explain the code and make it more understandable for humans.

• Use the # symbol for single-line comments.

  # This is a single-line comment
x = 10 # This comment explains what 'x' is