Dictionaries
Store values by name using key-value pairs.
A dictionary maps keys to values. Instead of looking items up by position, you look them up by name. Dictionaries are written with curly braces and colons.
Python
student = {"name": "Kabir", "age": 20, "city": "Bhopal"}
print(student["name"])
print(student)
print(len(student))Output
Kabir
{'name': 'Kabir', 'age': 20, 'city': 'Bhopal'}
3
Adding, changing and removing
Python
stock = {"apples": 10, "bananas": 6}
stock["oranges"] = 12 # add a new key
stock["apples"] -= 3 # change a value
del stock["bananas"] # remove a key
print(stock)
print(stock.get("grapes")) # missing key gives None
print(stock.get("grapes", 0)) # or a default you chooseOutput
{'apples': 7, 'oranges': 12}
None
0
Looping over a dictionary
.items() gives you each key and value together.
Python
prices = {"tea": 15, "coffee": 25, "samosa": 12}
for item, price in prices.items():
print(f"{item:<8} Rs {price}")
print(list(prices.keys()))
print(sum(prices.values()))Output
tea Rs 15 coffee Rs 25 samosa Rs 12 ['tea', 'coffee', 'samosa'] 52
Counting with a dictionary
A classic use is counting how often things appear.
Python
text = "the cat and the hat and the bat"
counts = {}
for word in text.split():
counts[word] = counts.get(word, 0) + 1
print(counts)Output
{'the': 3, 'cat': 1, 'and': 2, 'hat': 1, 'bat': 1}
Since Python 3.7, dictionaries remember the order in which keys were added.