AHS CODING CLUB

A list in Python is an ordered, mutable (changeable), and indexed collection of items.

Lists can contain any data type (e.g., int, str, list, dict, etc.).

Lists are dynamic (can grow or shrink in size).

Lists are defined using square brackets [].

Lists are created using square brackets [ ], and items inside the list are separated by commas.

fruits = ["Apple", "Banana", "Cherry"]
numbers = [1, 2, 3, 4, 5]
mixed = ["Hello", 42, True]  # A list can have different types of data!
                

You can pick items from the list using their position (index). Remember, Python starts counting from 0!

friends = ["Jake", "Emma", "Liam", "Sophia"]

print(friends[0])  # Prints "Jake"
print(friends[2])  # Prints "Liam"
                

You can update a list item like this:

fruits = ["Apple", "Banana", "Cherry"]
fruits[1] = "Orange"  # Changing "Banana" to "Orange"
print(fruits)  # Output: ['Apple', 'Orange', 'Cherry']
                

Use .append() to add an item at the end:

movies = ["Avatar", "Titanic"]
movies.append("Inception")
print(movies)  # Output: ['Avatar', 'Titanic', 'Inception']
                

Use .insert() to add an item at a specific position:

movies.insert(1, "Avengers")
print(movies)  # Output: ['Avatar', 'Avengers', 'Titanic', 'Inception']

Use .remove() to delete a specific item:

colors = ["Red", "Blue", "Green"]
colors.remove("Blue")
print(colors)  # Output: ['Red', 'Green']
                

Use .pop() to remove an item by index (or the last item if no index is given):

colors.pop(1)  # Removes "Blue" (index 1)
print(colors)
                

If you want to go through all items in a list, use a for loop:

games = ["Minecraft", "Fortnite", "Roblox", "Among Us"]
for game in games:
    print(game)
                

In the code above games is a list and each item in the list of games goes into the variable game that is created. It holds the value of the first item in the list the first time through the loop until it holds the last item and then exits the loop.

You can use this to loop if you want to do something with each loop item example printing it or

thislist = ["apple", "banana", "cherry"]
for i in range(len(thislist)):
  print(thislist[i])
                  
                

Use above to loop through the list if you need to use the index

Use the in keyword:

games = ["Minecraft", "Fortnite", "Roblox", "Among Us"]

if "Minecraft" in games:
    print("You love Minecraft!")
                

                  games = ["Minecraft", "Fortnite", "Roblox", "Among Us"]
                  #You can also check whether something is not in a list
                  if "Tetris" not in games:
                      #This print statement will execute because Tetris is not in games
                      print("You don't love Tetris!")
                                  

Want to put your list in order? Use .sort().

numbers = [5, 2, 9, 1, 3]
numbers.sort()  # Sorts from smallest to largest
print(numbers)  # Output: [1, 2, 3, 5, 9]
                

myList = []
myList.append("apples")
myList.append(2)
myList.append(3.5)
                    

What is a Function?

In programming, a function is a reusable block of code designed to perform a specific task. Instead of writing the same code multiple times, you can define a function once and call it whenever needed. The code in the function doesn't run unless the function is called in your program.

In video games, functions are widely used for actions like attacking, healing, jumping, or calculating scores.

Why Use Functions?

1. Reusability: Write the code once and reuse it multiple times. A player needs to heal, attack, or run. Instead of writing the same code repeatedly, use functions for each action.
2. Readability: Break down complex logic into smaller, manageable pieces.
3. Maintainability: Easier to update and debug specific parts of the code.
4. Organization: Group related logic together for better clarity.

How to Define a Functionss

1. Define the Function: Use the def keyword in Python.
2. Give the function a name
3. Open and close brackets
4. Use the colon after the brackets
5. Write the code that you want to execute when the function is called(used)
6. Call the Function: Use the function's name followed by parentheses.

def greet():
  print("Hello, welcome to Python!")
            

Once a function is defined, you can call (invoke) it by using its name followed by parentheses.

greet()
            

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


#Calling the function
greet("Alice")  # Calling the function with the argument "Alice"
greet("Bob")    # Calling the function with the argument "Bob"



            

A function can take multiple parameters. Just separate them with commas inside the parentheses.

def add(a, b):
  result = a + b
  print(f"The sum of {a} and {b} is {result}")

Calling function

add(5, 3) 

Make sure you have the variables in the correct order correct when calling the function. Also make sure the number of parameters in the definition and the number of arguments in the function call are the same.

You can give parameters default values, which are used if no argument is provided when the function is called.

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

You can call with arguments or without arguments

greet("Alice")  # Hello, Alice!
greet()         # Hello, Guest!
            

This Function Returns a Boolean.

def is_even(number):
    """This function checks if a number is even and returns True/False."""
    return number % 2 == 0

# Calling the function
print(is_even(4))  # Output: True
print(is_even(5))  # Output: False
            

Function Returns a String

def greet(name):
    """This function returns a greeting message."""
    return f"Hello, {name}! Welcome to Python."

# Calling the function
message = greet("Alice")
print(message)  # Output: Hello, Alice! Welcome to Python.
            

Functions can return any of the data types including dictionaries, lists, strings, etc. Lists are a great way to return multiple values.

While Loop

What is a while loop?

The while loop repeats a block of code as long as a specified condition is true. You must be careful to avoid infinite loops by ensuring that the loop's condition eventually becomes false.

Example:counting down with a while loop

count = 5
while count > 0:
  print(count)
  count -= 1
            

5
4   
3
2
1
            

Essential Tip: Always Initialize Variable You will be testing before entering the loop. And make sure this variable will change in the loop body so that eventually it will be false and the loop will stop otherwise you will have an infinite loop. Which will eventually crash your program.

By using True a literal. This value will not change and the loop will go on forever.

while True:
  print("Hello")

              

Whenever you have an infinite loop you must always have a condition that checks a variable and if that variable is true then you use a break statement

#Some use this instead of ininite Loop
running = True
while running:
   print("Something")

#They will have some code in the loop that will set running to false
# based on the checking of a variable or some type of input or interaction from 
#the users(example clicking the exit button (x) or using the input and checking to see whether user chose a particular option).
#There will be some sort of if statement to check the user's input and if that is true then there will be a break 
#statement inside of the if statement.

The for loop is used to iterate over a sequence, such as a list, tuple, dictionary, string, or a range of numbers. In each iteration, the loop variable takes the next value from the sequence.

# Loop from 0 to 4. Goes through the loop 5 times. When i is 0, 1, 2, 3, 4
#Loops from 0 to 4. 5 is not included. 
for i in range(5):
    print(i)
              

You can also specify start, stop, and step for the range:

# Loop from 2 to 10, stepping by 2. Up to 11 but not including 11
for i in range(2, 11, 2):
    print(i)
              

Loop Control Statements

• break: Exits the loop immediately.
• continue: Skips the current iteration and moves to the next.

Example with Break:

for i in range(10):
    if i == 5:
    break
    print(i)
    

0
1
2
3
4
    

Example with Continue:

for i in range(5):
    if i == 2:
      #It will not print when i is 2 as the continue statement will cause it to skip that step and go on to when i becomes 3.
      continue
      print(i)
              

You can have a for loop inside of another for loop and a while loop inside of a while loop or for loop iside of while loop and vice versa.

# Example: Printing a multiplication table using nested while loops
i = 1
while i <= 3:  # Outer while loop
    j = 1
    while j <= 3:  # Inner while loop
        print(f"{i} * {j} = {i * j}")
        j += 1
    i += 1
    print("------")



              

# Define a list of strings
words = ["Hello", "World", "Python"]

# Nested for loop to iterate over each character in each string
for word in words:       # Outer loop iterates over words (strings)
    for char in word:    # Inner loop iterates over characters in the word
        print(char, end=" ")  # Print characters in the same line with spaces
    print()  # Move to a new line after each word
              

Each outer loop iteration picks a string, and the inner loop iterates through each character in that string.

word = "Hello"
for letter in word:
  print(letter)
#Will print each individual letter 1 character at a time on its own line.

              

Print numbers 1 to 10

• Use a for loop or while loop to print numbers from 1 to 10.

Sum of numbers from 1 to n

1. Input: n
2. Output: Sum of all numbers from 1 to n.

Multiplication table

• Input: n
• Output: Print multiplication table for n (e.g., n x 1 to n x 10).
Print even numbers from 1 to 100

Reverse a string

1. Input: "hello"
2. Output: "olleh"

A dictionary (dict) in Python is an unordered, mutable, and indexed collection of key-value pairs.

Keys must be unique and immutable (e.g., str, int, tuple).

Values can be of any data type (e.g., int, str, list, even another dict).

person = {"name": "Bob", "age": 30}
#You can also create an empty dictionary and add values later on:
empty_dict = {}
  

#Raises KeyError if the key doesn’t exist.
#Using Square Brackets []
student = {"name": "Alice", "age": 21}
print(student["name"])  # Output: "Alice"
  

Using .get() Safer as you don't key error

print(student.get("name"))     # Output: "Alice"
print(student.get("grade"))    # Output: None (instead of KeyError)
print(student.get("grade", "N/A"))  # Output: "N/A" (default value). 
#In the last example the value on the right side of the comma you can 
#use as a default value if they key doesn't exist. It will create both the
#key and the value. 
  

Adding a Key Value Pair

student = {"name": "Alice"}
student["age"] = 21            # Adds new key "age"
student["name"] = "Bob"        # Updates "name"
  

Using .update()(Multiple Updates)

student.update({"name": "Charlie", "age": 22, "grade": "A"})
  

Deleting Items

del student["age"]             # Removes "age" key (raises KeyError if missing)
age = student.pop("age")       # Removes and returns value (safer)
student.clear()                # Empties the dictionary
  

.keys() Returns all keys

.values() Returns all values

.items() Returns key-value pairs as tuples

.copy() Creates a shallow copy. Create copy when don't want to change original.

.popitem() Removes & returns last inserted item (Python 3.7+)

Code Examples using methods

student = {"name": "Alice", "age": 21}

print(student.keys())    # Output: dict_keys(['name', 'age'])
print(student.values())  # Output: dict_values(['Alice', 21])
print(student.items())   # Output: dict_items([('name', 'Alice'), ('age', 21)])

for key, value in student.items():
  print(f"{key}: {value}")
  

Dictionaries can contain other dictionaries.

employees = {
  "emp1": {"name": "Alice", "age": 25},
  "emp2": {"name": "Bob", "age": 30}
}

print(employees["emp1"]["name"])  # Output: "Alice

Values can be of any data type (e.g., int, str, list, even another dict).

#Looping through keys and can get the item using the key
for key in d:
   print(d["key"])

#Items returns the key value pairs in a tuple which we do something with in the loop
for key, val in d.items():
    print(key, ": ", val)
    
            

d = {"a": 1, "b": 2}
"a" in d #Will return true if this key is in the dictionary
          

text = "apple banana apple orange banana apple"
words = text.split()
frequency = {}

for word in words:
    frequency[word] = frequency.get(word, 0) + 1

print(frequency)  # Output: {'apple': 3, 'banana': 2, 'orange': 1}
    
            

A module in Python is a file containing Python code (functions, classes, variables) that can be reused in other programs.

Modules help in organizing code into logical units.

They prevent naming conflicts and improve code reusability.

Example:

A file named math_operations.py can be a module containing math functions.

Another file can import and use these functions.

Types of Modules:

Built-in Modules (Pre-installed with Python)

• math (mathematical functions)
• random (random number generation)
• datetime (date and time handling)
• os (operating system interactions)

User defined Module

Third-party Modules (Installed via pip)

Another file can import and use these functions.

Import an Entire Module

#When import an entire module this way every function, object, class or variable you use has to have the module name and . before it.
import math
print(math.sqrt(16))  # Output: 4.0. sqrt is a function in the math module.
                

Import Specific Functions or Varibles

#When importing using this method you don't need to use module name followed by . 
#You can just use variable name or function name class name or object name directly
from math import sqrt, pi
print(sqrt(25))  # Output: 5.0
print(pi)        # Output: 3.141592653589793

                

Import with an alias

import numpy as np  #I have given numpy an alias(nickname). That I can use instead of numpy in my program
print(np.array([1, 2, 3]))  # Output: [1 2 3]

1. Create a .py file (e.g., calculator.py).
2. Define functions/variables inside it.
3. Import it in another script.

        #Saved in our module file called calculator.py
        def add(a, b):
          return a + b
        
        def subtract(a, b):
          return a - b
        

        #Our main file saved as main.py
        import calculator #How we import the calculator.py file with its functions
        
        print(calculator.add(5, 3))      # Output: 8
        print(calculator.subtract(5, 3)) # Output: 2
        

A tuple in Python is an immutable (unchangeable) and ordered collection of elements. Tuples are similar to lists but with one key difference: they cannot be modified after creation.

my_tuple = (1, 2, 3, 4, 5)
print(my_tuple)  # Output: (1, 2, 3, 4, 5)

#To create a tuple with one element, include a trailing comma.
single_element_tuple = (10,)  # Comma is necessary!
not_a_tuple = (10)  # This is just an integer

numbers = (10, 20, 30, 40, 50)

# Access elements by index
print(numbers[0])  # Output: 10
print(numbers[-1])  # Output: 50 (Last element)

# Slicing a tuple
print(numbers[1:4])  # Output: (20, 30, 40)
                      

a = (1, 2, 3)
b = (4, 5, 6)
print(a + b)  # Output: (1, 2, 3, 4, 5, 6)

print(a * 2)  # Output: (1, 2, 3, 1, 2, 3)