Class 22 — Wednesday March 4

You are so controlling

While I can go on – I do not repeat myself – Always a new way

---

Look both ways

• Back or ahead

---

Agenda

• Introduce while statement

• Introduce dict

---

Please take care

• Wash hands with soap frequently

• Try to stop touching your face with your hands

• If flying, check out this article

• Check out this CDC article on prevention and treatment.

---

To do

• Examine artifacts

• Examine dict module

• Examine collections epistle

• Homework

---

Redownload

• Module url.py

---

Examples

• Program guess_what.py

• Program even_odd.py

• Program romantic.py

• Program unromantic.py

• Program good_doggie.py

• Program que_dijiste.py

---

Maxims (among others)

• Read the problem in its entirety before problem solving

• Determine for yourself why the sample problem solutions are as they are

• Problem solve before you code

• Check whether your solution produces the same answers as the sample runs

• Check whether your solution matches problem specifications

---

To be considered

• How would you handle the problem of getting a yes or no reponse from a user, where case of the letters do not matter. Once gotten, the valid response is echoed (printed).

• Brainstorming

• Do we know ahead of time, how many often we need to loop?

• Are there action(s) that need to be done multiple times?

• Are there action(s) that need to be done once?

• Some possible runs

Enter (yes / no): yeah

Enter (yes / no): yeap

Enter (yes / no): tá

Enter (yes / no): כן

Enter (yes / no): ndiyo

Enter (yes / no): haan

Enter (yes / no): YeS

yes

Enter (yes / no): nah

Enter (yes / no): không

Enter (yes / no): nope

Enter (yes / no): aʻole

Enter (yes / no): ei

Enter (yes / no): NO

no

---

Whiling away

• Like many programming languages, Python provides more than one way to iterate actions (repeatedly execute). We are concerned here with its while looping offering.

• The while loop differs from the for loop in that the number of times it iterates is not based on the size of a list or range; instead, iteration is based on a logical test expression.

• The basic while state has the form:

while ( test expression ) :

  action

• When Python reaches a while loop, it will repeatedly execute the loop's actions as long as the test expression evaluates to true. When the test expression evaluates false, the program drops down to the statement following the loop. For example, consider yes_or_no.py

looking_for_a_yes_or_no = True

while ( looking_for_a_yes_or_no == True ) :

  reply = input( 'Enter (yes / no): ' )

  reply = reply.lower()

  if ( reply in [ 'yes', 'no' ] ) :

  looking_for_a_yes_or_no = False

print( reply )

• FYI: Python is one of the languages whose while statement also allows an optional else. The else action is executed once the test expression evaluates to false.

while ( test expression ) :

  action

else :

  action

---

Problem guess_what.py

• Play a guessing name with the user. The program is to determine what number the user has guessedl, where the possible numbers are from 0 to 100,000.

• Brainstorming

• How would you solve the problem if you were the guesser?

• Can we do this with a for loop? If, so what are some possible ways?

• Can we do this with a while loop? If, so what are some possible ways?

---

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., we typically associate apple with red and January 1st with New Year's Day.

• A dict is Python's software equivallent of a collection of associations.

• In particular, a dict is unnordered collection of associations.

• The elements of 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.

• len( flora_to_color ) is 6 because the definition of flora_to_color included six mappings.

• The brackets [] operator in conjunction with assignment can be used to put a mapping into a dict.

• The statement below adds the mapping 'lemon' to 'yellow'.

flora_to_color[ 'lemon' ] = 'yellow'

• The keys of a dict are always distinct. If there had already been a mapping with 'lemon' as the key, the above assignment would replace the association.

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

• 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.

• del d[k] removes k’s mapping in d.

• (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.

• d.keys() are the keys for d. There are no duplicates among the keys.

• d.values() are the values of the keys in d. There are duplicate values if more than one key maps to the same value.

• Information on a dict is always 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

---

Huh?

• dónde está mi lápiz

• donde esta mi lapiz

• hvor 是 该 tumili maleri av Munch

• est la baguette fraîche aujourd'hui

• est la baguette fraiche aujourd'hui

---

Problem que_dijiste.py

• Reads and prints the babelfish csv-based translation dictionary

{'aab': 'water', 'aamadam': 'came', 'aamadand': 'came', 'aamad': 'came', 'aamadi': 'came',

...

'wollen': 'want', 'wort': 'word', 'wo': 'where', 'y': 'and', 'yo': 'I', 'Yo': 'I', 'yun': 'wool', 'yün': 'wool', 'zahl': 'number', 'zauberformel': 'spell', 'zauberhaft': 'enchanting', 'zehn': 'ten', 'zeichen': 'characters', 'zeigt': 'show', 'ziba': 'beautiful', 'zur': 'to', 'zu': 'to', 'zwei': 'two', '是': 'is', '该': 'the'}

Next class — what we really want to do

Enter phrase to be translated: dónde está mi lápiz

where is my pencil

Enter phrase to be translated: est la baguette fraîche aujourd'

is the baguatte fresh today

Enter phrase to be translated: je %#@#&# ból svayam!!

I >%#@#&#< hurt myself >!!<

Enter phrase to be translated: hvor er den skriget maleri af Munch

where is the scream painting by Münch

Enter phrase to be translated: hacer 뭔가 frais oggi

do something cool today

• Brainstorming

• How should we store the translations?

• How should we store the input?

• How should we store the result?

• What times of loops do we need?

---

---

 

---

 

© 2020 Jim Cohoon

Resources from previous semesters are available.