Class 29 — Monday April 12

Moving on

Working Together – On a cautionary tale – New understandings

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Look both ways

• Back or ahead

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Parameter passing downloads

• Program cautionary.py

• Module tale.py

• Program up.py

• Module date.py

• Program alma.py

• Module mater.py

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Module self-testing downloads

• Module im_a_module.py

• Tester im_a_tester_program.py

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Next homework

• Module aid.py.

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Agenda

• Problem solve

• Consider parameter passing nuances

• Consider optional parameter nuances

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

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To do

• Examine next homework module aid.py.

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What the heck happens (PDF, slide show)

# program cautionary.py | # module tale.py

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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Now what the heck happens

# program up.py | # module date.py

import date | def f( x ) :

nbrs = [ 3, 1, 4 ] | n = len( x )

date.f( nbrs ) | for i in range( 0, n ) :

print( nbrs ) | x[ i ] = 0

  | return

• Does the above code print

[ 3, 1, 4 ]

• Or does the it print

[ 0, 0, 0 ]

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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 module 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 the string '__main__' if

  # you are running the file as a program

  # it is set to the name of the file if

  # the file is being imported

  abet.test_rotate()

  abet.test_rotate_k_times()

  abet.test_common()

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Module for next class aid.py — homework 25

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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🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.