Python Programming Iterating And Manipulating Collections Complete Guide

Python Programming: Iterating and Manipulating Collections

1. Introduction to Collections

Collections in Python are built-in datatypes that are used to store multiple items in a single variable. These collections can be categorized into mutable and immutable types:

• Mutable Collections: These can be modified after creation. Examples include lists and dictionaries.
• Immutable Collections: These cannot be modified after creation. Examples include tuples and sets.

2. Iterating Over Collections

Iterating over collections involves going through each item one by one. Python provides several methods for iteration:

• For Loop: The for loop is the most commonly used method for iterating over collections.

  # Iterating over a list
  fruits = ['apple', 'banana', 'cherry']
  for fruit in fruits:
      print(fruit)
  

  # Iterating over a dictionary
  student_grades = {'Alice': 85, 'Bob': 78, 'Charlie': 92}
  for student, grade in student_grades.items():
      print(f'{student}: {grade}')
  

• Enumerate Function: The enumerate() function adds a counter to an iterable and returns it as an enumerate object.

  fruits = ['apple', 'banana', 'cherry']
  for index, fruit in enumerate(fruits):
      print(f'{index}: {fruit}')
  

• Zip Function: The zip() function aggregates elements from each of the iterables.

  names = ['Alice', 'Bob', 'Charlie']
  grades = [85, 78, 92]
  for name, grade in zip(names, grades):
      print(f'{name}: {grade}')
  

3. Manipulating Collections with List Comprehensions

List comprehensions provide a concise way to create lists. They consist of brackets containing an expression followed by a for clause, then zero or more for or if clauses.

# Simple list comprehension
squares = [x**2 for x in range(10)]
print(squares)  # Output: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# Including a condition
even_squares = [x**2 for x in range(10) if x % 2 == 0]
print(even_squares)  # Output: [0, 4, 16, 36, 64]

4. Using Built-in Functions to Manipulate Collections

Python provides several built-in functions that are useful for collection manipulation:

• len(): Returns the number of items in a collection.

  fruits = ['apple', 'banana', 'cherry']
  print(len(fruits))  # Output: 3
  

• sorted(): Returns a new sorted list from the elements of any collection.

  fruits = ['banana', 'cherry', 'apple']
  sorted_fruits = sorted(fruits)
  print(sorted_fruits)  # Output: ['apple', 'banana', 'cherry']
  

• min()/max(): Return the smallest and largest item in a collection, respectively.

  grades = [85, 78, 92]
  print(min(grades))  # Output: 78
  print(max(grades))  # Output: 92
  

• sum(): Sums up the elements in a numeric collection.

  grades = [85, 78, 92]
  total = sum(grades)
  print(total)  # Output: 255
  

5. Modifying Collections

Depending on the collection type, you can add, update, or delete items:

• Lists:

  • Add items using append(), insert(), or extend().
  • Remove items using remove(), pop(), or del.

  fruits = ['apple', 'banana']
  fruits.append('cherry')         # ['apple', 'banana', 'cherry']
  fruits.insert(1, 'blueberry')   # ['apple', 'blueberry', 'banana', 'cherry']
  fruits.extend(['date', 'fig'])  # ['apple', 'blueberry', 'banana', 'cherry', 'date', 'fig']
  fruits.remove('banana')         # ['apple', 'blueberry', 'cherry', 'date', 'fig']
  fruits.pop()                    # ['apple', 'blueberry', 'cherry', 'date']
  del fruits[0]                   # ['blueberry', 'cherry', 'date']
  

• Dictionaries:

  • Add/Modify items using indexing.
  • Remove items using del or pop().

  student_grades = {'Alice': 85, 'Bob': 78}
  student_grades['Charlie'] = 92                        # {'Alice': 85, 'Bob': 78, 'Charlie': 92}
  student_grades['Alice'] = 88                          # {'Alice': 88, 'Bob': 78, 'Charlie': 92}
  del student_grades['Bob']                             # {'Alice': 88, 'Charlie': 92}
  charlie_grade = student_grades.pop('Charlie')         # {'Alice': 88}, charlie_grade = 92
  

• Sets:

  • Add items using add().
  • Remove items using remove(), discard(), or pop().

  fruits = {'apple', 'banana', 'cherry'}
  fruits.add('blueberry')                                 # {'apple', 'banana', 'cherry', 'blueberry'}
  fruits.remove('banana')                                 # {'apple', 'cherry', 'blueberry'}
  fruits.discard('date')                                  # {'apple', 'cherry', 'blueberry'}
  a_fruit = fruits.pop()                                  # {'cherry', 'blueberry'}, a_fruit = 'apple'
  

6. Common Operations with Collections

• Concatenation:

  list1 = [1, 2, 3]
  list2 = [4, 5, 6]
  combined_list = list1 + list2
  print(combined_list)  # Output: [1, 2, 3, 4, 5, 6]
  

• Membership Testing:

  fruits = ['apple', 'banana', 'cherry']
  print('banana' in fruits)  # Output: True
  

• Slicing:

  numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  slice_numbers = numbers[2:6]
  print(slice_numbers)  # Output: [3, 4, 5, 6]
  

• Copying: