1. Nate Brunelle Today: Dictionaries
CS1110
Nate Brunelle
Today: Dictionaries

2. Questions?

3. Collections Order doesn’t matter, No Repetition
Order Matters, Repetition ok
Examples:
String
List
Tuple
Range
Counting starts at 0
collection[index] gives a specific value in the collection
Order doesn’t matter, No Repetition
Examples:
Set
Dict
Map
Table

4. Set
Things are unordered
Cannot have repetition

5. Dict A set of key:value mappings d = { } # How we create one
d[‘name’] = 1 # How we insert somthing
d[‘name’] # Access something

6. Dict is like variables Gives names to values Create using =
Reassign using =
Easy to go from name to a value
Very hard to go from value to name

7. Dict is like a List Index to access members Key to access members
Key can be any immutable type
No rules for values of keys
To add in a new thing: d[key] = …
Index to access members
Index must be an int
Indexes cannot be skipped
To add in a new thing: lst.append(…)

8. Using a dict as a Collection
d.keys()
Gives a list of all of the keys in the dict
The key is the thing in square brackets
The “word”
When you use a dict as a collection, it defaults to this
E.g.: for thing in d
d.values()
Gives a list of all the values in the dict
The value is what you get when you access using a key
The “definition”
d.items()
Gives a list of all (key, value) tuples in the dict

9. Key
Value
Bananas
12.0
Gloves
29.0
Suit
100.0
Bananas 10.0 Gloves 29.0 Suit Bananas 2.0 If that thing was in the dictionary: add to that value Else: add that thing to the dictionary, with value equal to the cost