Python: Working with Dictionaries
Learn about dictionaries in Python, which are key-value pair collections that are unordered, indexed and changable.
September 17, 2022 · 4 min read
Unlike all other collection types, dictionaries strictly contain key-value pairs.
Dictionaries are collections that are unordered, changeable, and are indexed.
They are similar to lists but instead of the index being a number, you can instead use the key to access the element.
Creating a Dictionary
Here's how you create a dictionary:
queens = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
print(queens)Output:
{'city': 'New York City', 'state': 'New York', 'country': 'United States'}Accessing Items
Items in a dictionary can be accessed using the key.
queens = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
print(queens["city"])Output:
New YorkAdding Items to Python Dictionary
You can add items to a dictionary by setting a new key-value pair, like this:
company = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
company["name"] = "ABC Inc"
print(company)Output:
{'city': 'New York City', 'state': 'New York', 'country': 'United States', 'name': 'ABC Inc'}Update Items in Python Dictionary
Dictionaries allow you to change the value of an item if you refer to it directly:
company = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
company["city"] = "London"
company["country"] = "GB"
print(company){'city': 'London', 'state': 'New York', 'country': 'GB'}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:
queens = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
for key in queens:
value = queens[key]
print("Key: " + key + " Value: " + value)Output:
Key: city Value: New York City
Key: state Value: New York
Key: country Value: United StatessChecking if a Key Exists
You can check if a key exists inside a dictionary like this:
queens = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
print("city" in queens)Output:
TrueRemoving Items
You can remove items from a dictionary by using the pop() function and providing the key. Here's how that looks:
queens = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
queens.pop("city")
print(queens){'state': 'New York', 'country': 'United States'}Dictionary Length
You can get the number of items that exist in your dictionary by using the len() function:
queens = {
"city": "New York City",
"state": "New York",
"country": "United States"
}
print(queens)
print(len(queens))Output:
{'city': 'New York City', 'state': 'New York', 'country': 'United States'}
3