Dictionaires

Introduction to Dictionaries in Python

• Dictionaries are built-in data structures in Python.

• They store data in key/value pairs.

• Accessing values is done through keys, not numeric indices as with lists.

What is a Dictionary?

• A dictionary is an indexed container.

• Elements are indexed by keys rather than positions (0, 1, 2, etc.).

• Each entry in a dictionary consists of a pair: a key and a value.

Example of Using a Dictionary

• Consider storing student names:

  • Using a list:

    • students = ["Paul", "Peng", "Yasmin", "Maria"]

    • Accessing elements requires knowing the index:

    • To retrieve "Peng":

      • students[1] gives "Peng".

    • To retrieve "Maria":

      • students[3] gives "Maria".

Transition to Dictionaries

• A dictionary provides a more efficient approach:
  - students = {1: "Paul", 5678: "Peng"}

  • Keys are the student IDs; values are the names.

  • Add more pairs:

    • students[9876] = "Yasmin"

    • students[6543] = "Maria".

Accessing Values in a Dictionary

• To access "Peng":

  • Use the key: students[5678] returns "Peng".

• To access "Maria":

  • Use: students[6543] returns "Maria".

Dictionary Methods

• You can retrieve all keys in a dictionary:

  • students.keys() returns all keys.

• Retrieve all values:

  • students.values() returns all values.

Characteristics of Dictionaries

• The order of elements is not significant; they are indexed by keys, not by position.

• Keys must be unique to identify each pair uniquely.

• Values can be of any type, including strings, integers, or even lists.

Advanced Usage of Values

• Values can be complex data structures:

  • For example, a string containing grades:

    • Value could be formatted as: "name;grade1;grade2;..."

  • This allows the dictionary to function similarly to a small database.

Conclusion

• The video covered the dictionaries in Python, highlighting their ability to store data indexed by unique keys in key/value pairs.

• A dictionary provides a flexible way to structure data, where both keys and values can be tailored to meet various needs.