CS 1112: Fall 2020

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).

Questions

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 ) :
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

Program 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.

Questions

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?

Program romantic.py

Get a roman numeral and determine its integer equivalent

Three sample program runs

Enter Roman numeral: V
5

Enter Roman numeral: d
500

Enter Roman numeral: 0
Unknown

Program unromantic.py

Get a word and print its English equivalent

Sample 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.

Program even_odd.py

Introduce the Python dict data structure

Two sample 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

Program 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

Questions

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

Program 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

Questions

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?

Resources from previous semesters are available.