Modifying Dictionaries

Changing a value

To update a value, use square brackets with the key and assign a new value:


person = {"name": "Alice", "age": 30, "city": "New York"}
 
person["age"] = 31
print(person)  # Output: {'name': 'Alice', 'age': 31, 'city': 'New York'}

Adding a new key-value pair

Adding a new key works exactly the same way — if the key doesn’t exist yet, Python creates it:


person["occupation"] = "Engineer"
print(person)
# Output: {'name': 'Alice', 'age': 31, 'city': 'New York', 'occupation': 'Engineer'}

Removing a key-value pair

You have two options for removing a pair:

del — removes the key-value pair directly:


del person["city"]
print(person)  # Output: {'name': 'Alice', 'age': 31, 'occupation': 'Engineer'}

pop() — removes the pair and gives back the value, so you can use it:


occupation = person.pop("occupation")
print(occupation)  # Output: Engineer
print(person)      # Output: {'name': 'Alice', 'age': 31}

Use del when you just want to remove something. Use pop() when you need the value before it’s gone.

Looping over a dictionary

Use .items() to loop over both keys and values at the same time:


person = {"name": "Alice", "age": 31, "city": "New York"}
 
for key, value in person.items():
    print(key, "->", value)
 
# Output:
# name -> Alice
# age -> 31
# city -> New York

You can also loop over just the keys or just the values:


for key in person:
    print(key)          # name, age, city
 
for value in person.values():
    print(value)        # Alice, 31, New York

Example: Color palette

Dictionaries are a natural fit for storing named colors — something you’ll do in the Generative Art project:


palette = {
    "background": (15, 15, 30),
    "primary":    (255, 100, 80),
    "secondary":  (80, 180, 255),
    "accent":     (255, 220, 50),
}
 
# Access a color by name
print(palette["primary"])   # (255, 100, 80)
 
# Loop to print all colors
for name, color in palette.items():
    print(f"{name}: {color}")

Try it out

main.py

Output