Class 11 – Friday, February 26

Odds, ends, and beginnings

Lest we go forward — We cannot come back again — But beware of baths

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Look both ways

• Back or ahead

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Agenda

• Extend string functionality

• Extend print() function functionality

• Foreshadow nested loops

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Downloads

• Program combine_replicate.py

• Program slice_of_pie.py

 

• Program secret_decoder.py

 

• Program thats_printastic.py

• Program c_looper.py

 

• Program going_rowing.py

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To do list

• Reveal one of your super power(s)

• Share a selfie

• Review class artifacts.

• Complete current homeworks

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Program combine_replicate.py

• Shows two string operators

### operator + performs concatenation

a = fire

b = fighter

a + b = firefighter

### * operator produces repeated concatenation

m = Wahoo-Wah!

n = 3

m * n = Wahoo-Wah!Wahoo-Wah!Wahoo-Wah!

n * m = Wahoo-Wah!Wahoo-Wah!Wahoo-Wah!

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Program slice_of_pie.py

• Introduces the sequence slicing operator :

• Two possible program runs

Enter favorite pie: anchovies and garlic

Enter two indices: 3 15

s: anchovies and garlic

i: 3

j: 15

s[ i ]: h

s[ j ]: a

s[ i : j ]: hovies and g

s[ i : ]: hovies and garlic

s[ : j ]: anchovies and g

s[ : ]: anchovies and garlic

Enter favorite pie: strawberry rhubarb

Enter two indices: 12 14

s: strawberry rhubarb

i: 12

j: 14

s[ i ]: h

s[ j ]: b

s[ i : j ]: hu

s[ i : ]: hubarb

s[ : j ]: strawberry rhu

s[ : ]: strawberry rhubarb

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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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Program thats_printastic.py

• Introduce print() optional closing parameter end="..."

• The optional end="..." parameter for a print() function allows changing from its default action of starting the next print on a new line.

• Program run

Wa-Hoo-Wa

Rah-Rah-Rah

Wa-Hoo-Wa!Rah-Rah-Rah

Wa-Hoo-Wa! Rah-Rah-Rah

t-a-t-t-a-r-r-a-t-t-a-t-

s a i p p u a k i v i k a u p p i a s

saippuakivikauppias

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Program c_looper.py

• Task

• For a user-supplied n, prints a line of the form

row : 0 1 2 ... n-1

• Some program runs

Enter number of columns: 5

row : 0 1 2 3 4

Enter number of columns: 12

row : 0 1 2 3 4 5 6 7 8 9 10 11

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Program dataset_intro.py

• Demonstrates looping through a dataset in different ways

• Program run

table: [['A', 'B', 'C'], ['D', 'E', 'F'], ['G', 'H', 'I'], ['J', 'K', 'L', 'M']]

the table has 4 rows

row ['A', 'B', 'C'] has 3 columns

row ['D', 'E', 'F'] has 3 columns

row ['G', 'H', 'I'] has 3 columns

row ['J', 'K', 'L', 'M'] has 4 columns

row 0 : ['A', 'B', 'C']

row 1 : ['D', 'E', 'F']

row 2 : ['G', 'H', 'I']

row 3 : ['J', 'K', 'L', 'M']

 

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🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.