Week 2

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Week 2: Data Structures & Exception Handling

1. Lists, Tuples, Dictionaries, Sets

Lists

1. Basic List Operations

   my_list = [1, 2, 3, 4, 5]
   my_list.append(6)  # Add an element
   my_list.remove(2)  # Remove an element
   print(my_list)  # Output: [1, 3, 4, 5, 6]

2. List Indexing and Slicing

   numbers = [10, 20, 30, 40, 50]
   print(numbers[1])  # Output: 20
   print(numbers[-1])  # Output: 50
   print(numbers[1:4])  # Output: [20, 30, 40]

Tuples

1. Tuple Basics

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

2. Immutable Nature of Tuples

   my_tuple = (10, 20, 30)
   # my_tuple[0] = 100  # This will raise an error since tuples are immutable

Dictionaries

1. Creating and Accessing Dictionary Elements

   student = {"name": "Alice", "age": 25, "city": "New York"}
   print(student["name"])  # Output: Alice

2. Adding and Removing Elements from Dictionary

   student["grade"] = "A"  # Adding a new key-value pair
   del student["age"]  # Deleting a key
   print(student)

Sets

1. Creating and Using Sets

   my_set = {1, 2, 3, 4, 5}
   my_set.add(6)  # Adding an element
   my_set.remove(3)  # Removing an element
   print(my_set)  # Output: {1, 2, 4, 5, 6}

2. Set Operations (Union, Intersection, Difference)

   set1 = {1, 2, 3}
   set2 = {3, 4, 5}
   print(set1 | set2)  # Union: {1, 2, 3, 4, 5}
   print(set1 & set2)  # Intersection: {3}
   print(set1 - set2)  # Difference: {1, 2}

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2. List & Dictionary Comprehensions

1. List Comprehension Example

   squares = [x ** 2 for x in range(1, 6)]
   print(squares)  # Output: [1, 4, 9, 16, 25]

2. Dictionary Comprehension Example

numbers = [1, 2, 3, 4, 5]
squared_dict = {num: num ** 2 for num in numbers}
print(squared_dict)  # Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

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3. Exception Handling (try-except-finally)

1. Basic Exception Handling

   try:
       x = 5 / 0
   except ZeroDivisionError:
       print("Cannot divide by zero!")

2. Handling Multiple Exceptions

   try:
       num = int(input("Enter a number: "))
       print(10 / num)
   except ValueError:
       print("Invalid input! Please enter a number.")
   except ZeroDivisionError:
       print("Cannot divide by zero!")

3. Using finally Block

   try:
       file = open("data.txt", "r")
       content = file.read()
   except FileNotFoundError:
       print("File not found!")
   finally:
       print("Closing file (if opened).")

4. Using else in Exception Handling

   try:
       result = 10 / 2
   except ZeroDivisionError:
       print("Cannot divide by zero!")
   else:
       print("Division successful:", result)

5. Raising Custom Exceptions

   def check_age(age):
       if age < 18:
           raise ValueError("You must be 18 or older.")
       return "Access granted!"
   
   try:
       print(check_age(16))
   except ValueError as e:
       print(e)

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4. File Handling (Reading/Writing Files, CSV, JSON)

1. Writing to a File

   with open("example.txt", "w") as file:
       file.write("Hello, Python File Handling!")

2. Reading from a File

   with open("example.txt", "r") as file:
       content = file.read()
       print(content)

3. Reading a File Line by Line

   with open("example.txt", "r") as file:
       for line in file:
           print(line.strip())

4. Writing and Reading CSV Files

   import csv
   
   data = [["Name", "Age"], ["Alice", 25], ["Bob", 30]]
   
   with open("people.csv", "w", newline="") as file:
       writer = csv.writer(file)
       writer.writerows(data)
   
   with open("people.csv", "r") as file:
       reader = csv.reader(file)
       for row in reader:
           print(row)

5. Writing and Reading JSON Files

import json

data = {"name": "Alice", "age": 25, "city": "New York"}

with open("data.json", "w") as file:
    json.dump(data, file, indent=4)

with open("data.json", "r") as file:
    loaded_data = json.load(file)
    print(loaded_data)

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