Assignment 23 — function implementation that manipulate lists

Wednesday, November 2

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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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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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