Class 22 — Wednesday March 24

Look at the map

• Asian lives matter — We are a single people — That celebrate you

---

Look both ways

• Back or ahead

---

Agenda

• Introduce dict

---

To do

• Examine artifacts

• Examine dict module documentation

• Examine collections epistle

• Examine while epistle

• Homework

---

Examples

• Program url.py (Please redownload)

• Program romantic.py

• Program unromantic.py

• Program even_odd.py

• Program good_doggie.py

• Program robotomy.py

---

Some datasets

• romans.csv

• babelfish

---

Problem romantic.py

• Get a roman numeral and determine its integer equivalent

Some program runs

Enter Roman numeral: V

5

Enter Roman numeral: d

500

Enter Roman numeral: 0

Unknown

---

Problem unromantic.py

• Get a word and print its English equivalent

Some program runs

RecursionError: maximum recursion depth exceeded during compilation

---

Discussion

• Repeat the word carrot ten times out loud

• The human brain is great with associations; e.g., many of us associate apple with red, sky with blue, and programming with fun.

• A dict is Python's software equivallent of a collection of associations. In particular, a dict is an unnordered collection of associations.

• The elements of a dict are called mappings. A mapping associates one object (called the key) with another object (called the value).

• The literal for an empty dict is {}.

• A literal mapping is written using the : to separate the key with its value. For example, the variable flora_to_color defined below is a dict that associates flora with colors.

flora_to_color = { 'spruce': 'green', 'apple': 'red', 'shamrock': 'green',

  'banana': 'yellow', 'potato': 'brown', 'eggplant': 'purple' }

• The len() function works on a dict. For example, len( flora_to_color ) is 6, because the definition of flora_to_color specified six mappings.

• The brackets [] operator in conjunction with assignment can be used to put a mapping into a dict. For example, the statement below adds the mapping 'lemon' to 'yellow'.

flora_to_color[ 'lemon' ] = 'yellow'

• The keys of a dict are always distinct. So, the following statement

flora_to_color[ 'potato' ] = 'golden'

would cause flora_to_color to lose its association of mapping potato to brown — its associaton with 'potato' is now only to golden.

• As our flora_to_color example shows, the values of a dict are not necessarily unique.

• Python dict's have functions keys() and values() for getting a hold of keys and values.

the_keys = flora_to_color.keys()

the_values = flora_to_color.values()

While there are never any duplicates in the keys, depending upon the dictionary there may be duplicates in the values.

• Other information about dict objects are listed below. In the below, assume that d is a dict.

• d.get(k) returns the value that key k maps to in d. If there is no such value, returns None.

• d[k] returns the value that key k maps to in d. If there is no such value, an exception (error) occurs.

• (k in d) indicates whether k is a key value in d.

• (k not in d) indicates whether k is not a key value in d.

• d.clear() removes all mappings in d.

• del d[k] removes k’s mapping in d.

• Information on a dict is available in the module documentation section of the website.

• Additional information on collections is in general is available in the collections epistile.

---

Problem even_odd.py

• Introduce the Python dict data structure

Some program runs

Enter a number: 3

3 odd

Enter even or odd: even

a number is even if its remainder divided by 2 is 0

Enter a number: 6

6 even

Enter even or odd: odd

a number is odd if its remainder divided by 2 is 1

---

Problem good_doggie.py

• For a series of dog information requests, the program reports what it knows about the dog.

• Its dog information data source is located at URL

http://www.cs.virginia.edu/~cs1112/datasets/csv/puppies.csv

• Brainstorming

• How should we store the dog information?

• How do we get and store the input?

• How many times do we set up the dog information

• What times of loops do we need?

• Sequential

• Nested

• Mixture of nested and sequential

---

Problem robotomy.py

• Determine what happens when a robot comes knocking on a door.

• If the door is locked, the robot should be instructed to turn around.

• If the door is instead unlocked, the robot should be instructed to open the door and enter the room. Before entering, the robot should determine whether the light is off. If it is off, the robot should be instructed to first turn on the light.

• Observation

• There is one procedure to perform if the door is locked, another to perform if it is unlocked

• The procedure to perform if the door is unlocked, requires analysis whether the light is on.

• Some program runs

Door (locked / unlocked): locked

Turn around

Door (locked / unlocked): Unlocked

Open the door

Light (on / off): on

Enter the room

Door (locked / unlocked): unlocked

Open the door

Light (on / off): Off

Turn on the light

Enter the room

---

Raining cats and dogs (English idiom)

 

---

🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.