Dictionaries

Dictionary Basics

• Dictionaries collect data values, but assign them to another piece of data, instead of to an index
• 'Indexes' for dictionaries are called keys
• Both pieces of data together are a 'key-value pair'
• Dictionaries are contained within braces
• Keys and values are separated by colons
• Key-value pairs are separated by commas
• Order does not matter in dictionaries, therefore they cannot be sliced or manipulated by index position
• Dictionaries are a mutable data type
• Example: PID = {'hair':'brown', 'height':'5"8'', 'name':'John Doe'}

Functions to use with Dictionaries

• Use loops along with keys(), values(), and items() to return list-like values

• dictionaryname.keys() returns all key values when looped
• dictionaryname.values() returns only the values when looped
• dictionaryname.items() returns the key-value pairs when looped

• Use get() to find an item or return a fallback if the value does not exist

• Get() takes two arguments - key value and a fallback if the key doesn't exist
• dictionaryname.get('key-value', 'fallback-value')

• Use setdefault() to set a value for a key if it doesn't currently have a value

• This takes two arguments - the key to check for and the value to set if the key doesn't exist
• It is useful to ensure that a key exists and avoid errors
• dictionaryname.setdefault('key-value', 'value-to-set')

• The Pretty Printing module provides a cleaner display of values

• Import the module with import pprint
• pprint.pprint(dictionaryname) is useful for nested dictionaries and when printing to the string
• It displays key-value pairs, one per line
• pprint.pformat(dictionaryname) directs the values to a string instead of printing it to the screen