Class 29 — Monday, November 1

Listing

To be, not to be — That is the question I ask – The answer, to be

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Look both ways

• Back or ahead

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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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Pillow download

• Program test-pillow.py

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Parameter passing downloads

• Program up.py

• Module date.py

• Program my.py

• Module gosh.py

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Optional parameters downloads

• 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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Remembering the past

# 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

• We know from a prior class that it prints

London Paris

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Puzzle me this

# program my.py | # module gosh.py

import gosh | def f( x ) :

nbrs = [ 3, 1, 4 ] | x = [ 0, 0, 0 ]

gosh.f( nbrs ) | return

print( nbrs ) |

• Does the above code print

[ 3, 1, 4 ]

• Or does the it print

[ 0, 0, 0 ]

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Now what's happening

# 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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Optional parameters

• Python supports functions having optional parameters

print( "hurry", end=" " )

print( "up", end=" " )

Produces

hurry up

• Module alma.py demonstrates a function chant() with two optional parameters.

def chant( msg='Wahoo Wah', n=3 ) :

  for i in range( 0, n ) :

  print( msg )

  return

• program mater.py demonstrates uses of chant()

alma.chant()

...

alma.chant( msg='Hip hip hooray!' )

...

alma.chant( n=5 )

...

alma.chant( 'We are CS 1112', 1 )

• A run of program mater.py produces output.

chanting with no parameters

Wahoo Wah

Wahoo Wah

Wahoo Wah

chanting with message parameter set

Hip hip hooray!

Hip hip hooray!

Hip hip hooray!

chanting with number of repetitions set

Wahoo Wah

Wahoo Wah

Wahoo Wah

Wahoo Wah

Wahoo Wah

chanting with arguments for message and repetition parameters

We are CS 1112

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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 24

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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