DICTIONARIES

• Dictionary: object that stores a collection of data
    • Each element consists of a key and a value
        • Often referred to as mapping of key to value
        • Key must be an immutable object
    • To retrieve a specific value, use the key associated with it
    • Format for creating a dictionary
dictionary = {key1:val1, key2:val2}

ADD AND DELETE DICTIONARY

• Dictionaries are mutable objects
• To add a new key-value pair: dictionary[key] = value     • If key exists in the dictionary, the value associated with it will be changed
• To delete a key-value pair: del dictionary[key]>     • If key is not in the dictionary, KeyError exception is raised

DICTIONARY NUMBER OF ELEMENTS AND MIXING DATA TYPES

• len function: used to obtain number of elements in a dictionary
• Keys must be immutable objects, but associated values can be any type of object
    • One dictionary can include keys of several different immutable types
• Values stored in a single dictionary can be of different types

CREATING AN EMPTY DICTIONARY AND USING FOR LOOP

• To create an empty dictionary:
    • Use {}
    • Use built-in function dict()
    • Elements can be added to the dictionary as program executes
• Use a for loop to iterate over a dictionary
    • General format: for key in dictionary:
for key in dictionary:

SOME DICTIONARY METHODS