Creating a Dictionary

• Dictionaries are created by using a set of curly braces ({})
• The dict() constructor can also be used to create a dictionary data type

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}
dictExample2 = dict({
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
})
dictExample3 = {"code": "4061CEM", "title": "Programming and Algorithms", "leader": "Ian Cornelius"}

Data Types of Items in a Dictionary (1)

• The items of a dictionary can be any data type
  • i.e. it can be a mixture of data types such as booleans, strings or integers

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}
dictExample2 = {
    "code": 4061,
    "faculty": "CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius",
    "running": True
}

Data Types of Items in a Dictionary (2)

• Dictionaries can also store other dictionaries inside themselves

dictExample3 = {
    "code": 4061,
    "faculty": "CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius",
    "running": True,
    "resources": {
        "book1": {
            "author": "Heineman, G.T., Pollice, G. and Selkow, S.",
            "title": "Algorithms in a nutshell: A practical guide.",
            "year": "2016"
        }
    }
}

Accessing Dictionary Items (1)

• The items in a dictionary can be accessed by referring to its key inside a set of square brackets ([])

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1["code"]

Accessing Dictionary Items (2)

dictExample1 = {
    "code": 4061,
    "faculty": "CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius",
    "running": True,
    "resources": {
        "book1": {
            "author": "Heineman, G.T., Pollice, G. and Selkow, S.",
            "title": "Algorithms in a nutshell: A practical guide.",
            "year": "2016"
        }
    }
}

dictExample1["resources"]["book1"]["author"]

Accessing Dictionary Items (3)

• The items in a dictionary can also be accessed by using the get() function, and a key

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.get("code")
dictExample1.get("leader")

Accessing Dictionary Items (4)

List of Dictionary Keys

• A list of keys that are present in a dictionary can be retrieved using the keys() function
• The list of keys can be considered to be a view of the dictionary
  • therefore, any changes made to the dictionary will be rectified in the list of keys

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.keys()

Accessing Dictionary Items (5)

List of Dictionary Values

• A list of values that are present in the dictionary can be retrieved using the values() function
• The list of values can be considered to be a view of the dictionary
  • therefore, any changes made to the dictionary will be rectified in the list of values

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.values()

Accessing Dictionary Items (6)

List of Dictionary Items

• A tuple of items that are present in the dictionary can be retrieved using the items() function
  • Each tuple returned is the key and value that is present in the dictionary
• The tuple of items can be considered to be a view of the dictionary
  • Therefore, any changes made to the dictionary will be rectified in the tuple of items

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.items()

Modifying a Dictionary (1)

• As items are ordered and indexed, they are modifiable; otherwise known as being mutable

Adding an Item i

• Adding an item to the dictionary can be done using the update() function
  • when using this method, you must provide a key:value pair in the function

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.update({"running": True})

Modifying a Dictionary (2)

Adding an Item ii

• The same key:value pair can be added using the square brackets ([]) notation

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1["running"] = True

Modifying a Dictionary (4)

Removing Items from a Dictionary i

• Items can be removed from a dictionary using the pop() function
  • this will remove the item from the list using its key

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.pop("title")

Modifying a Dictionary (5)

Removing Items from a Dictionary ii

• An item can also be removed from a list by using the popitem() function
  • this will remove the last inserted item

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.popitem()

Modifying a Dictionary (6)

Removing Items from a Dictionary iii

• An item can also be removed from a dictionary by its key using the del keyword

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

del dictExample1["title"]

Modifying a Dictionary (7)

Clearing a Dictionary

• A dictionary can be cleared of all its items, but still reserve its memory location by using the clear() function
  • this will empty the contents of a dictionary and leave it empty, symbolised by just the curly brackets ({})

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

dictExample1.clear()

Modifying a Dictionary (8)

Deleting a Dictionary

• The entire dictionary can be deleted and removed from the memory using the del keyword

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

del dictExample1

Copying a Dictionary

• The method of copying a dictionary by using dict2 = dict1 is incorrect
  • this method creates a reference to dict1 and not an actual copy; therefore any changes made in dict1 will occur in dict2
• The correct process of copying a list can be achieved by the copy() function or the dict() constructor itself

dictExample1 = {
    "code": "4061CEM",
    "title": "Programming and Algorithms",
    "leader": "Ian Cornelius"
}

copyDictExample1 = dictExample1.copy()
copyDictExample2 = dict(dictExample1)