Python Data Structures Lecture Notes

Introduction

• Overview of important topics in Module 2
• Focus on Lists, Strings, and Dictionaries as built-in data types in Python.

Lists in Python

• Definition: Lists are a built-in data type used to store collections of items.
• Characteristics:
  • Versatile data structures.
  • Elements can be of any data type (numbers, strings, etc.).

Basic Operations on Lists

1. Adding Values:
   • Append: Add value at the end.
   • Insert:
     • Syntax: my_list.insert(index, value)
     • Example: my_list.insert(1, 'A')
2. Removing Values:
   • Remove: Removes first occurrence of a value.
   • Pop: Removes value at specified index and returns it.
     • Example: my_list.pop(index)
3. Finding Values:
   • Use in operator or index() method.
   • Example: if 'item' in my_list:
4. Sorting Lists:
   • Use sort() function to create a sorted copy without modifying the original.

List vs Tuple

• List: Mutable, can change contents. Suitable for collections of items needing modification.
• Tuple: Immutable, contents cannot change, more efficient in terms of performance.
• Conversion Example:
  • To create a tuple from a list: tuple(my_list)

Strings in Python

• Definition: Strings are built-in data types used to represent text sequences.
• Strings are surrounded by single or double quotation marks.

Common String Methods

1. upper(): Converts all characters to uppercase.
   • Example: text.upper()
2. replace(): Replaces occurrences of a word in the string.
   • Example: text.replace('old', 'new')

Traversing a List

• Definition: Visiting each element of the list for operations (printing, modifying, searching).
• Methods to Traverse:
  1. For Loop:
     • Example: for item in my_list:
  2. While Loop:
     • Example: while index < len(my_list):
  3. List Comprehension:
     • Example: [item**2 for item in my_list]
  4. Enumerate: Track both index and value.
     • Example: for index, value in enumerate(my_list):**

Dictionaries in Python

• Definition: Unordered collection of key-value pairs, also known as associative arrays or hash maps.
• Characteristics:
  • Accessed by keys, not index.
  • Example: my_dict = {'key': 'value'}

Key Methods in Dictionaries

1. items(): Returns a view of all key-value pairs.
2. keys(): Returns a view of all keys in the dictionary.
3. values(): Returns a view of all values in the dictionary.

Differences between Dictionaries and Lists

• List: Ordered collection, accessed by index.
• Dictionary: Unordered collection, accessed by keys. Elements have no specific order.

Conclusion

• Encouragement to keep learning about Python
• Next sessions will cover additional topics. Happy learning!