Dictionaries

Last half of Chapter 5

Dictionary

• A sequence of key-value pairs– Key is usually a string or integer– Value can be any python object

• There is no order to the elements– So, there isn't a first or a last element– Python uses its own algorithm to order elements

(for efficient access)• You access values by using the key.

Dictionary operations

• Creating an empty dictionary:D = {}

• Creating a dictionary with string-float pairsD2 = {"ABC":42.9, "DEF":13.8, "GHI":-19.1}

• Getting a list of keys or valuesD2.keys() # Returns ["ABC", "GHI", "DEF"] or something like this.

• Getting a list of valuesD2.values() # Returns [42.9, -19.1, 13.8]

Dictionary Index'ing

• Using an existing elementprint(D2["ABC"])

• Changing a value for an existing keyD2["ABC"] = 100.3

• Adding a new valueD2["XYZ"] = 0.0

Note how this looks the same as modifying.

Dictionary examples

• [Using integers as a key]• [Reiner Tile Sets…]