Class 10 – Wednesday, February 24

Listing

Lest we go forward — Without knowing about lists — We would be wanting

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Look both ways

• Back or ahead

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Agenda

• Make loops right

• Provide you more background on list basics

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Important survey

• Please take this voluntary survey

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For the fun of it

• Reveal one of your super power(s).

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Alert

• Anyone who asks me today about a function sum() earns negative ducks.

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To do list

• Review class artifacts.

• Review epistles

• Complete homework

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Downloads

• Program list_support.py

• Program list_building.py

• Program wowzers.py

• Program summing.py

• Program secret_decoder.py

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Lists

• Tell me about them

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Program list_support.py

• Task

• Show some basic list operations

s = "we are in it together"

values = [ ]

stuff = [ 'abc', 1112, 2.71, ]

digits = [ 3, 1, 4, 1, 5, 9, 2, 6 ]

words = s.split()

vlen = len( values )

slen = len( stuff )

dlen = len( digits )

wlen = len( words )

print( "size of", values, "=", vlen )

print( "size of", stuff, "=", slen )

print( "size of", digits, "=", dlen )

print( "size of", words, "=", wlen )

dmax = max( digits )

dmin = min( digits )

wmax = max( words )

wmin = min( words )

print( "max of", digits, "=", dmax )

print( "min of", digits, "=", dmin )

print( "max of", words, "=", wmax )

print( "min of", words, "=", wmin )

• Program run

size of [] = 0

size of ['abc', 1112, 2.71] = 3

size of [3, 1, 4, 1, 5, 9, 2, 6] = 8

size of ['we', 'are', 'in', 'it', 'together'] = 5

max of [3, 1, 4, 1, 5, 9, 2, 6] = 9

min of [3, 1, 4, 1, 5, 9, 2, 6] = 1

max of ['we', 'are', 'in', 'it', 'together'] = we

min of ['we', 'are', 'in', 'it', 'together'] = are

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Program list_building.py

• Task

• Re-demonstrate list function append() and built-in function range()

values = [ ]

values.append( "u" )

values.append( "v" )

values.append( "a" )

values.append( "!" )

values.append( " " )

values.append( "u" )

values.append( "v" )

values.append( "a" )

values.append( "!" )

print( "values =", values )

ints = []

for i in range( 0, 10 ) :

  ints.append( i )

print( "ints =", ints

• Program run

values = ['u', 'v', 'a', '!', ' ', 'u', 'v', 'a', '!']

ints = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

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Program wowzers.py

• Task

• Loop through a string, list of words, and a list of numbers

• Analyze a list using built-in functions

• Possible program run

Enter your favorite color: teal

Enter some names: willy evander aurelius ann

color = teal

names = ['willy', 'evander', 'aurelius', 'ann' ]

numbers = [12, 7, -11, -12, 59]

T

E

A

L

Willy

Evander

Aurelius

Ann

-12

-7

11

12

-59

t e a l

['willy', 'evander', 'aurelius', 'ann' ]

[5, 7, 8, 3]

length of longest name: 8

first alphabetically = ann

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Numeric list paradigm — program summing.py

• Task

• Demonstrates accumulation to sum a list of numbers

reply = input( 'Enter a list of numbers: ' )

slist = reply.split()

nlist = []

for s in slist :

  nbr = int( s )

  nlist.append( nbr )

# by accumulation get the sum of the numbers

total = 0

for nbr in nlist :

  total = total + nbr

# print summation

print( "sum(", nlist, "):", total )

• Some program runs

Enter a list of numbers: 3 1 4 1 5 9

sum( [3, 1, 4, 1, 5, 9] ): 23

Enter a list of numbers: 58 2 37 16 99 1 9 23

sum( [58, 2, 37, 16, 99, 1, 9, 23] ): 245

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Chrestomathics — program secret_decoder.py

• Scenario

• Separately get an input code phrase and list of indices. Determine the hidden message by using the indices to peek into the code phrase. For example, suppose the code phrase equals

'abcdefghijklmnopqrstuvwxyz-'

and the indices are

[ 4, 8, 26, 4, 8, 26, 14 ]

• Then the hidden message is

'ei-ei-o'

Because s[ 4 ] equals 'e';   s[ 8 ] equals 'i';   s[ 14 ]; equals 'o';   and s[ 26 ] equals '-'.

• Algorithm

• Get the code phrase that contains hidden message.

• Clean up reply to get code phrase with no leading or trailing whitespace.

• Print the code phrase.

• Get the list of indices (as string) for peeking into code phrase.

• Convert reply into a list of numeric strings.

• Build one-by-one the list of indices out of the numeric strings .

• Print the list of indices.

• Build secret message (string) by peeking into code phrase using the indices.

• Print secret message.

• Some program runs

Enter code phrase: computer

Code phrase: computer

Enter indices: 3 6 5

Indices: [3, 6, 5]

Hidden message: pet

Enter code phrase: gosh look what the cat is up to now

Code phrasee: gosh look what the cat is up to now

Enter indices: 24 5 17 17 27 23 32 0

Indices: [24, 5, 17, 17, 27, 23, 32, 0]

Hidden message: sleeping

Enter code phrase: ‐abcdefghijklmnopqrstuvwxyz‐

Code phrase: ‐abcdefghijklmnopqrstuvwxyz-

Enter indices: 12 15 22 5 27 9 19 0 1 12 12 27 14 5 5 4

Indices: [12, 15, 22, 5, 27, 9, 19, 0, 1, 12, 12, 27, 14, 5, 5, 4]

Hidden message: love‐is‐all‐need

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Hoos got your back — food insecurity

• Nationwide more than 10% of college students are not able to afford nutrious food. This problem occurs at UVA also. I am aware of two sources at UVA to help out.

• The Engineering School has a food pantry in Thornton A121. It operates on the honor system and is meant to help students with need.

• The unversity assists with the Community Food Pantry in the Runk Green Room. See the website for details.

• If you find yourself experiencing some financial hardships, please consider talking with anyone in the Undergraduate Programs Office. They can help you find even more resources.

• If you can pay it forward, please help by donating items or money to either pantry.

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Coney Island Cyclone roller coaster

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Willy Mays

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Marcus Aurelius

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Evander of Pallantium

 

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🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.