Dictionaries

What Are Dictionaries?

  • Dictionaries are used to store data values in key-value pairs. They are one of Python's built-in data types, alongside lists, tuples, and sets.

Creating a Dictionary:

  • Dictionaries are created using curly brackets {} or the dict() constructor.

    python
    thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)
    • Output: {'brand': 'Ford', 'model': 'Mustang', 'year': 1964}

Properties of Dictionaries:

  • Ordered (Python 3.7+): Items have a defined order.
  • Changeable: You can change, add, or remove items.
  • No Duplicates: Dictionaries cannot have duplicate keys.

Examples:

  • Accessing Items:

    • Use the key to access its value.

      python
      thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict["brand"])
      • Output: Ford
  • Adding Items:

    • Add a new key-value pair.

      python
      thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

thisdict["color"] = "red"
print(thisdict)
      • Output: {'brand': 'Ford', 'model': 'Mustang', 'year': 1964, 'color': 'red'}
  • Changing Items:

    • Change the value of an existing key.

      python
      thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964,
  "color": "red"
}

thisdict["year"] = 2020
print(thisdict)
      • Output: {'brand': 'Ford', 'model': 'Mustang', 'year': 2020, 'color': 'red'}
  • Removing Items:

    • Remove a key-value pair using the pop() method or the del keyword.

      python
      thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 2020,
  "color": "red"
}

thisdict.pop("model")
print(thisdict) 

del thisdict["color"]
print(thisdict)
      • Output: {'brand': 'Ford', 'year': 2020, 'color': 'red'}
      • Output: {'brand': 'Ford', 'year': 2020}

Dictionary Methods:

  • Dictionaries come with various built-in methods such as:
    • clear(): Removes all elements.
    • copy(): Returns a copy of the dictionary.
    • fromkeys(): Returns a dictionary with specified keys and values.
    • get(): Returns the value of the specified key.
    • items(): Returns a list containing a tuple for each key-value pair.
    • keys(): Returns a list containing the dictionary's keys.
    • pop(): Removes the element with the specified key.
    • popitem(): Removes the last inserted key-value pair.
    • update(): Updates the dictionary with the specified key-value pairs.
    • values(): Returns a list of all the values in the dictionary.

Exercises:

  1. Create and Print a Dictionary:

    • Create a dictionary of your favorite car with keys such as brand, model, and year. Print the dictionary.

      python
      mycar = {
  "brand": "Tesla",
  "model": "Model S",
  "year": 2021
}
print(mycar)
      • Output: {'brand': 'Tesla', 'model': 'Model S', 'year': 2021}
  2. Access and Update Items:

    • Access and print the value of the "model" key. Update the "year" to 2022 and print the updated dictionary.

      python
      mycar = {
  "brand": "Tesla",
  "model": "Model S",
  "year": 2021
}
print(mycar["model"])  # Output: Model S
mycar["year"] = 2022
print(mycar)
      • Output: {'brand': 'Tesla', 'model': 'Model S', 'year': 2022}
  3. Add and Remove Items:

    • Add a new key-value pair for color and remove the "model" key. Print the updated dictionary.

      python
      mycar = {
  "brand": "Tesla",
  "model": "Model S",
  "year": 2021
}
mycar["color"] = "blue"
mycar.pop("model")
print(mycar)
      • Output: {'brand': 'Tesla', 'year': 2021, 'color': 'blue'}

Summary:

  • Dictionaries are versatile and powerful for storing and managing key-value pairs in Python. They allow you to quickly access, modify, and iterate over data. Practice creating, accessing, and updating dictionaries to become proficient in using them!