Class 27 — Wednesday, October 27

Moving on

Working Together – On a cautionary tale – New understandings

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Look both ways

• Back or ahead

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Agenda

• Being functional

• Convert specifications dealing with strings into working functions

• Mindful collaboration

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Download (available at start of class)

• Program stripping.py

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• Module go.py

• Tester program forth.py

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• Module tale.py

• Tester program cautionary.py

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• Module quad.py

• Tester program riga.py

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Post class

• Review musings.

• Try CodingBat.

• Complete Homework.

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Program stripping.py

• Background

• The string function strip() can remove more that just leading and trailing whitespace in producing its return string.

• The strip() function can take a string as an argument. Any leading or trailing character in the argument string is not part of the return string

• Some program runs

Enter text: abra-cadabra

Enter stripping characters: a

bra-cadabr

Enter text: abra-cadabra

Enter stripping characters: A

abra-cadabra

Enter text: abra-cadabra

Enter stripping characters: bar

-cad

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Module go.py — function ints( ns )

• Parameter ns is a string that composed of zero or more integer substrings and nothing else.

• The function returns a list of integers corresponding to the integer substrings in ns.

• FYI: The following strings do not meet the specification for the ints() parameter ns, as they all contain at least non-integer substring.

bad1 = "abc"

bad2 = "3 def 4 ghi"

bad3 = "3.14"

• FYI: The following the variable definitions all meet the specification for the ints() parameter ns, as they are composed of zero or more integer substrings and nothing else.

ns1 = " 3 "

ns2 = "12 11 -63"

ns3 = "31 415 92 653 5 9"

ns4 = " "

• The ints() tester when given those strings as arguments to the function should produce the following output.

ints( ns1 ): [3]

ints( ns2 ): [12, 11, -63]

ints( ns3 ): [31, 415, 92, 653, 5, 9]

ints( ns4 ): []

• Possible algorithm

• ???

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Module go.py — function parse_phone_string( pn )

• Parameter pn is a string representing a USA phone number with an area code but without a country code. The first three digits in pn are the area code; the next three digits in pn are the prefix; and the last four digits in pn are the line number.

• The function returns a three-element integer list. The first element of the list is the pn area code in integer form; the middle element of the list is the pn prefix in integer form; the last element of the list is the pn line number in integer form

• Consider the following phone number strings

pn1 = "(201) 867-5309"

pn2 = "636-555-3226"

pn3 = "212 555 2368 (help line)"

pn4 = "888.799.9666 (customer service)"

• The parse_phone_string() tester when given those strings as arguments to the function should produce the following output.

parse_phone_string( pn1 ): [201, 867, 5309]

parse_phone_string( pn2 ): [636, 555, 3226]

parse_phone_string( pn3 ): [212, 555, 2368]

parse_phone_string( pn4 ): [888, 799, 9666]

• Possible algorithm

• ???

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Parameter passing nuances

• For your examimation: PDF or slide show.

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You got to see it, to believe it

• Pair programming

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Module quad.py

• Defines four functions for cleaning up lists of strings. Program riga.py performs simple testing of quad.py.

• Observation: none of the function implementations need nested for-loops.

• Requirement: none of the functions are allowed to modify their parameters.

• Recommendtion: review string and list documentation

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Suppose the following definitions are in effect below

test1 = ['AbCdE', 'ABCDE', '!"#\'x$&)|}~', '- x -_', 'AAcc', ' ', 'x\n']

test2 = ['\tx X']

test3 = []

test4 = ['a', 'B', 'r', 'A', 'c', 'a', 'D', 'a', 'B', 'r', 'a']

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Function to_lower( strings )

• Parameter strings is a list of strings.

• Returns a new list whose elements are lower case versions of those in strings.

• Given the above definitions of test1, test2, test3, and test4, the following is the expected invocation results for to_lower().

to_lower( test1 ) = ['abcde', 'abcde', '!"#\'x$&)|}~', '- x -_', 'aacc', ' ', 'x\n']

to_lower( test2 ) = ['\tx x']

to_lower( test3 ) = []

to_lower( test4 ) = ['a', 'b', 'r', 'a', 'c', 'a', 'd', 'a', 'b', 'r', 'a']

• Observation: an accumulator is needed. Lower-case versions of elements of strings need to be added to the accumulator one-at-a-time.

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Function cleanup( strings )

• Parameter strings is a list of strings.

• Returns a new list whose elements correspond to the elements in strings with leading and trailing extraneous characters (punctuation or whitespace) removed.

• The following constants are defined for the function

PUNCTUATION = '''!"#$%&'()*+,-./:;<=>?@[]^_`{|}~'''

WHITE_SPACE = ' \t\n\r\v\f'

EXTRANEOUS = PUNCTUATION + WHITE_SPACE

• Given the above definitions of test1, test2, test3, and test4, the following is the expected invocation results for cleanup().

cleanup( test1 ) = ['AbCdE', 'ABCDE', 'x', 'x', 'AAcc', '', 'x']

cleanup( test2 ) = ['x X']

cleanup( test3 ) = []

cleanup( test4 ) = ['a', 'B', 'r', 'A', 'c', 'a', 'D', 'a', 'B', 'r', 'a']

• Observation: an accumulator is needed. Stripped versions of elements of strings need to be added to the accumulator one-at-a-time.

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Function unique( strings )

• Parameter strings is a list of strings.

• Returns a new version of strings without any duplicate values.

• Given the above definitions of test1, test2, test3, and test4, the following is the expected invocation results for unique().

unique( test1 ) = ['AbCdE', 'ABCDE', '!"#\'x$&)|}~', '- x -_', 'AAcc', ' ', 'x\n']

unique( test2 ) = ['\tx X']

unique( test3 ) = []

unique( test4 ) = ['a', 'B', 'r', 'A', 'c', 'D']

• Observation: an accumulator is needed. The elements of strings need to be added to the accumulator one-at-a-time if they are not already there.

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Function canonical( strings )

• Parameter strings is a list of strings.

• Returns a new list cleaned up lower case version of strings without duplicates. It should be obvious that making use of functions cleanup(), to_lower(), and unique() should be helpful.

• To ensure that you do make use of functions cleanup(), to_lower(), and unique() should be helpful, no loops are allowed in canonical() code.

• Because functions to_lower() and cleanup() both have the potential for returns lists with duplicates, function canonical() needs to make use of unique() after using to_lower() and cleanup().

• Given the above definitions of test1, test2, test3, and test4, the following is the expected invocation results for canonical().

canonical( test1 ) = ['abcde', 'x', 'aacc', '']

canonical( test2 ) = ['x x']

canonical( test3 ) = []

canonical( test4 ) = ['a', 'b', 'r', 'c', 'd']

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Module quad.py musings

• Functions to_lower() and cleanup() seem similar.

• Both functions want to return a new list, where there will be a separate entry for each string in their string list parameter strings.

• The new lists must be accummulated.

• For each string in strings, a conversion is produced and the conversion is added to the accummulator.

• In WWAHD speak

Create a new empty list

For each string in strings do

— Get a converted version of the string

— Add conversion to the new list

Hand back completed new list

• Function unique() has similarities to functions to_lower() and cleanup().

• Needs to build and return a new list.

• The new list needs to be accumulated.

• Needs to consider each string in the string list parameter strings for the accumulation.

• However, it does not need to do a conversion. Instead, it needs to individually check each string in strings whether to add it to the accumulator.

• In WWAHD speak

Create a new empty list

For each string in strings do

— Test whether string needs to be added the new list. If so, add string to new list

Hand back completed new list

• The job of function canonical() is to produce a cleaned up, lowercase version of strings with no duplicates. It should be obvious that making use of functions cleanup(), to_lower(), and unique() should be helpful.

• Use one of three functions to start the conversion process.

• Pass its result to a second of the functions.

• Pass that result to the third function to produce the desired canonical result.

Because both cleanup() and to_lower() have the potential to return duplicates, unique() needs to be the third function. It is up you to determine whether one of the other two needs to be first.

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Slide show

 

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