Python Collections

Introduction

• Explanation of different types of collections in Python.
• Focus on general-purpose collections: Lists, Sets, Tuples, and briefly Dictionaries.
• Definition: Collection = single variable used to store multiple values.

Lists

• Definition: A list is surrounded by square brackets [].
• Example:
  • fruits = ['Apple', 'Orange', 'Banana', 'Coconut']
• Naming Convention: Use plural for collection variables (e.g., fruits).

Accessing Elements

• Use index operator: 0-based indexing.
• Example:
  • fruits[0] returns 'Apple'.
  • fruits[1] returns 'Orange'.
  • Attempting to access an out-of-range index raises an error.

Slicing

• : fruits[0:3] returns ['Apple', 'Orange', 'Banana'].
• Step parameter: fruits[::2] returns every second element.
• Reverse: fruits[::-1] returns list in reverse order.

Iteration

• Use a for loop to iterate: for fruit in fruits:
• Replace X with descriptive variable name for readability.

Methods and Functions

• Use dir() to list methods: print(dir(fruits)).
• Help function: help(fruits) provides descriptions for methods.
• Common methods:
  • append(): Add an element.
  • remove(): Remove an element.
  • sort(): Sort the list.
  • clear(): Clear all elements.
• Length: Use len(fruits) to return the number of elements.
• Check for existence: if 'Apple' in fruits: returns a boolean.

Characteristics

• Lists are ordered, changeable, and allow duplicates.
• Example of modifying a list: fruits[0] = 'Pineapple'.

Sets

• Definition: A set is surrounded by curly braces {}.
• Example: fruits = {'Apple', 'Orange', 'Banana', 'Coconut'}.

Characteristics

• Sets are unordered and immutable (cannot change values).
• No duplicates allowed.

Methods

• Use dir() for methods and help() for descriptions.

• Common methods:

  • add(): Add an element.
  • remove(): Remove an element.
  • clear(): Clear all elements.

• Length: Use len() to find out how many elements in a set.

• Example codes:

  • Adding: fruits.add('Pineapple').
  • Removing: fruits.remove('Apple').

Characteristics Summary

• Sets are unordered, immutable, and cannot have duplicates.

Tuples

• Definition: A tuple is surrounded by parentheses ().
• Example: fruits = ('Apple', 'Orange', 'Banana', 'Coconut').

Characteristics

• Tuples are ordered and unchangeable but allow duplicates.
• Faster than lists: Use when you need an ordered collection without changes.

Methods

• Limited methods: count() and index().
• Example: fruits.index('Apple') returns the index of 'Apple'.

Iteration

• Tuples are iterable; you can use a for loop to iterate.

Summary of Collections

1. Lists: Ordered, changeable, duplicates allowed.
2. Sets: Unordered, immutable, duplicates not allowed.
3. Tuples: Ordered, unchangeable, duplicates allowed, faster than lists.
4. Dictionaries: To be discussed next.

• Overall understanding: Collections in Python serve to group multiple values efficiently, each with its unique strengths and proper use cases.