Class 29 — October 29

Moving on

Working Together – On a cautionary tale – New understandings

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Look both ways

• Back or ahead

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Module quad.py

• Musings on problem solving

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Nuance downloads

• Program cautionary.py

• Module tale.py

• Program wipe.py

• Module zero.py

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Agenda

• Consider module development

• Problem solve

• Consider parameter passing nuances

• Show if ( __name__ == '__main__' ) statement for aiding testing

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Test 2

• November 13

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To do

• Examine parameter passing nuances.

• Complete current homework module quad.py.

• Consider optional election forecasting homework.

• Examine next homework module aid.py.

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What the heck happens (PDF, slide show)

import tale | def f( x, y ) :

city1 = 'London' | rmbr = x

city2 = 'Paris' | x = y

tale.f( city1, city2 ) | y = rmbr

print( city1, city2 ) | return

• Does the above code print

London Paris

• Or does the it print

Paris London

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Module self-testing downloads

• Module im_a_module.py

• Tester im_a_tester_program.py

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Tester statement if ( __name__ == '__main__' )

• Along with some built-in functions, Python provides each Python file with a built-in variable __name__.

• For a Python file being imported by another Python file, the variable is set to the name of imported file.

• For a Python file being run as a program, the variable is set to '__main__'

• With this if statement, a module can provide self-testing if run as a program.

• Why do you care about this functionality?

• Such testing will also be part of the modules for ongoing homework and future tests

• Homework aid.py uses the if ( __name__ == '__main__' ) statement to support testing using abet.py.

if ( __name__ == '__main__' ): # __name__ is a built in python variable.

  import abet # it is set to __main__ if you are running

  # that module as a program

  # it is set to the name of the module

  # if it is being imported

  abet.test_rotate()

  abet.test_rotate_k_times()

  abet.test_common()

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Module quad.py musings

• Functions to_lower() and cleanup() seem very similar to me.

• 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 list 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() also has some 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, a test 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 with a second of the functions.

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

What is left to do is figure out does it make a difference which of functions cleanup(), to_lower(), and unique() should be applied first, second, and third. I will just say not any order of the three will work in general.

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Module for next class aid.py — homework 27

Function rotate( x )

• Updates list x by moving the last element of list x (if any) to the beginning of list x. This type of list transformation is often called a circular shift.

• In carrying out its action, the function modifies the contents of the list x in place (e.g., by list-modification methods like pop(), append(), and insert(), or by directly modifying individual elements of list x.

• The function returns None.

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Function rotate_k_times( x, k )

• Updates list x by performing k circular shifts.

• In carrying out its action, the function modifies the contents of the list x in place.

• The function returns None

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Function common( x, y )

• Returns a new list whose elements are those elements in x that are also in y. The ordering of elements in the return list should reflect their ordering in x.

• The function does not modify parameters x and y in any way.

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Slide show

 

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© 2020 Jim Cohoon

Resources from previous semesters are available.