Lecture Notes: Python Collections

General Purpose Collections

• Four main types: Lists, Sets, Tuples, and (later) Dictionaries.
• Purpose: Collections act as a single variable that stores multiple values.

Lists

• Syntax: Values enclosed in square brackets [].
• Characteristics:
  • Ordered and changeable.
  • Allows duplicates.
• Accessing Elements:
  • Use index operator, e.g., fruits[0] for the first element.
  • Supports slicing, e.g., fruits[0:3].
  • Indexes start at 0.
• Iterating: Use a for loop, e.g., for fruit in fruits:.
• Common Methods:
  • append(): Adds element at the end.
  • remove(): Removes first occurrence of a value.
  • insert(index, element): Inserts an element at a specified index.
  • sort(): Sorts the list.
  • reverse(): Reverses the order of the list.
  • clear(): Removes all elements.
  • count(value): Counts occurrences of a value.
  • index(value): Returns index of the first occurrence.
• Length: Use len(list).
• Checking Membership: Use in operator, e.g., 'apple' in fruits.

Sets

• Syntax: Values enclosed in curly braces {}.
• Characteristics:
  • Unordered and immutable (elements can't be changed).
  • No duplicates allowed.
• Modifying:
  • add(element): Adds an element.
  • remove(element): Removes a specific element.
  • pop(): Removes a random element.
  • clear(): Removes all elements.
• Accessing Elements:
  • Cannot use indexing.
• Checking Membership: Use in operator.
• Length: Use len(set).

Tuples

• Syntax: Values enclosed in parentheses ().
• Characteristics:
  • Ordered and unchangeable.
  • Allows duplicates.
  • Faster than lists.
• Accessing Elements:
  • Can use indexing, e.g., fruits[0].
• Common Methods:
  • count(value): Counts occurrences of a value.
  • index(value): Returns index of the first occurrence.
• Length: Use len(tuple).
• Checking Membership: Use in operator.

Summary

• Lists: Ordered, changeable, allows duplicates.
• Sets: Unordered, immutable but can add/remove elements, no duplicates.
• Tuples: Ordered, unchangeable, allows duplicates, faster than lists.
• General: Collections are like single variables for multiple values.