From last class

• What is the difference between a list and tuple in Python?

  • While the language does not inforce lists to be homogeneous, it is generally a good idea to use them as such

  • tuples are immutable

    >>> mytuple = ( 1, 'one' )
    >>> mytuple[1]
    one
    >>> mytuple[1] = 'two'
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: 'tuple' object does not support item assignment

Sorted Dictionaries

• sorted
• key functions

Elements of a text-based game

• Game data stored on disk
• Load data from disk to memory
• Manipulate in-memory data based on user actions
• Write data back to disk

Representing an Environment

• record-jar

  files/rooms.rjar

  name: SURGE 104C
  description: a generic classroom
  items: desk,chalk,a mysterious note
  north: SURGE Study Area
  %%
  name: SURGE Study Area
  description: an open space
  items: vending machine
  south: SURGE 104C

  Using a record-jar parser I wrote we can load this file into Python:

  >>> from record_jar_reader import load_records
  >>> rooms = load_records( open('rooms.rjar', 'r') )
  >>> from pprint import pprint #to pretty-print Python objects
  >>> pprint(rooms)
  [{'description': 'a generic classroom',
    'items': 'desk,chalk,a mysterious note',
    'name': 'SURGE 104C',
    'north': 'SURGE Study Area'},
   {'description': 'an open space',
    'items': 'vending machine',
    'name': 'SURGE Study Area',
    'south': 'SURGE 104C'}]
  >>>

  Notice, we get a list of dicts. If we wanted to print a list of room names we would have to iterate over the items in the list and retreive the ‘name’ field of each.

  >>> for room in rooms:
  ...     print(room['name'])
  ...
  SURGE 104C
  SURGE Study Area
  >>>

  The cleanest way to obtain a list of room names is with list comprehension:

  >>> names = [ room['name'] for room in rooms ]
  >>> print(names)
  ['SURGE 104C', 'SURGE Study Area']
  >>>

  A more traditional for loop to do the same thing would look like

  >>> names = []
  >>> for room in rooms:
  ...     names.append(room['name'])
  ...
  >>> print(names)

• YAML

  files/rooms.yaml

  SURGE 104C: 
      desc: a generic classroom
      items: [ desk, chalk, a mysterious note ] 
      north: SURGE Study Area
  SURGE Study Area: 
     desc: an open space 
     items: [ vending machine ]
     south: SURGE 104C

  Assuming we write the description to a file named rooms.yaml:

  >>> import yaml
  >>> rooms = yaml.load( open('rooms.yaml', 'r') )
  >>> rooms
  {'SURGE 104C': {'desc': 'a generic classroom',
    'items': ['desk', 'chalk', 'a mysterious note'],
    'north': 'SURGE Study Area'},
   'SURGE Study Area': {'desc': 'an open space',
    'items': ['vending machine'],
    'south': 'SURGE 104C'}}

  Now we get a dict in which the keys are the names of the rooms and the values are each a dict with key/value pairs for the keys “desc”, “items”, etc.

  This representation is convenient to get a list of rooms:

  >>> rooms.keys()

  Or obtain the list of items in a particular room

  >>> rooms['SURGE 104C']['items']

• JSON

  If we have a file rooms.yaml already, let’s not make our life any harder. Use Python to convert from one format to another:

  >>> import yaml
  >>> import json
  >>> rooms = yaml.load( open('rooms.yaml') )
  >>> with open('rooms.json', 'w') as fp:
  ...    json.dump(rooms, fp, indent=4, separators=(',', ':'))

  Results in a file named ‘rooms.json’ with

  files/rooms.json

  {
      "SURGE 104C":{
          "desc":"a generic classroom",
          "items":[
              "desk",
              "chalk",
              "a mysterious note"
          ],
          "north":"SURGE Study Area"
      },
      "SURGE Study Area":{
          "desc":"an open space",
          "items":[
              "vending machine"
          ],
          "south":"SURGE 104C"
      }
  }

  Note, if we didn’t care about readability of the text file we could have omitted the indent and separators parameters to the json.dump call resulting in a file with

  files/rooms_inline.json

  {"SURGE 104C": {"north": "SURGE Study Area", "desc": "a generic classroom", "items": ["desk", "chalk", "a mysterious note"]}, "SURGE Study Area": {"desc": "an open space", "south": "SURGE 104C", "items": ["vending machine"]}}

Zork

A web-based port of Zork is available. Give it a spin.