Dictionaries

Dictionaries are collections that are unordered, changeable, and are indexed. They are Python's implementation of a key-value pair collection. They are similar to lists but instead of the index being a number, you can use the key to access the element instead.

Basically an actual dictionary but in code.

Creating a Dictionary

Here's how you create a dictionary:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

print(queens)

BASH
{'city': 'New York City', 'state': 'New York', 'country': 'United States'}

Accessing Items

The syntax for accessing items in a dictionary is similar to the syntax for accessing items in a list except that you use the key instead of the index:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

print(queens["state"])

BASH
New York

Adding Items

You can add items to a dictionary by setting a new key-value pair, like this:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

queens["organization"] = "United Nations"

print(queens)

BASH
{'city': 'New York City', 'state': 'New York', 'country': 'United States', 'organization': 'United Nations'}

Changing Items

Dictionaries allow you to change the value of an item if you refer to it directly:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

queens["state"] = "New Jersey"

print(queens["state"])

BASH
New Jersey

Looping through a Dictionary

You can iterate through the keys of a dictionary, and then use that key to get the value. Here's how:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

for key in queens:
    value = queens[key]
    print("Key: " + key + " Value: " + value)

BASH
Key: city Value: New York City
Key: state Value: New York
Key: country Value: United States

Alternatively, you can use the items() function to accomplish the same thing like this:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

for key, value in queens.items():
    print("Key: " + key + " Value: " + value)

BASH
Key: city Value: New York City
Key: state Value: New York
Key: country Value: United States

Checking if a Key Exists

You can check if a key exists inside a dictionary like this:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

print("city" in queens)
print("town" in queens)

BASH
True
False

Removing Items

You can remove items from a dictionary by using the pop() function and providing the key. Here's how that looks:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

queens.pop("state")

print(queens)

BASH
{'city': 'New York City', 'country': 'United States'}

Dictionary Length

You can get the number of items that exist in your dictionary by using the len() function:

PYTHON
queens = {
    "city": "New York City",
    "state": "New York",
    "country": "United States"
}

print(len(queens))

BASH
3

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