Class 9 – Monday, September 14

Do that again

Did you not expect – The repetition to come – Did you not expect

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Look both ways

• Back or ahead

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Agenda

• Looping

• List chrestomathics

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Downloads

• Program kinda_stringy.py

• Program wordy.py

• Program on_average.py

• Program again_and_again.py

• Program m_and_ns.py

• Program n_and_ms.py

• Program inty.py

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To do list

• Review class artifacts.

• Read the epistle on lists.

• Check out my documentation for the list module.

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Program kinda_stringy.py

Task

• Prompt, get, and individually print out the letters of a user-supplied three-character string.

• Prompt, get, and individually print out the letters of a user-supplied character string

Realization

• A loop is not necessary to handle the first input, as the number of characters to process is known when the program is being written.

• A loop is necessary to handle the second input, as the number of characters to process is not known when the program is being written.

• The loop to individually process the characters of the second input needs to done one thing each character, print it out.

Two possible program runs

Enter a three-letter string: abc

a

b

c

Enter a string: am too

a

m

t

o

o

Enter a three-letter string: def

d

e

f

Enter a string: are not

a

r

e

n

o

t

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Program wordy.py

Task

• Prompt and get text.

• Echo text to user.

• Echo word list to user.

• Report the length of the words one per line.

Realizations

• Because the number of words is not know when the program is being written, a loop is needed to process the words.

• The loop needs to do two things for each word: compute its length and print it out.

Some program runs

Enter text: All hoos got your back

Supplied text = All hoos got your back

words = ['All', 'hoos', 'got', 'your', 'back']

All : 3

hoos : 4

got : 3

your : 4

back : 4

Enter text: It was a dark and stormy night

Supplied text = It was a dark and stormy night

words = ['It', 'was', 'a', 'dark', 'and', 'stormy', 'night']

It : 2

was : 3

a : 1

dark : 4

and : 3

stormy : 6

night : 5

Enter text:

Supplied text =

words = []

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Program on_average.py

Task

• Examines a list of user-supplied words and reports determine average word length.

Realizations

• Because the number of words is not know when the program is being written, a loop is needed to process the words.

• To compute the average word length, need to know the number of words and the sum of the word lengths.

• The loop needs to two things for each word: compute its length and add its length to a running total.

• The running total needs to be initialized before the loop.

Two program runs

Enter text: over the hill and through the dale

Average word length: 4.0

Enter text: row row row your boat

Average word length: 3.4

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Program again_and_again.py

Task

• Prompt and get user-supplied text

• Prompt, get, and convert to integer, a user-supplied integer.

• Print requested text requested number of times.

Realizations

• Because the requested number of times is not know when the program is written, a loop is needed.

• The loop should perform the same actio each time through the loop, print the input text.

Two possible program runs

Enter string to be printed: once again

Enter number of times to be printed: 3

once again

once again

Enter string to be printed: one more time

Enter number of times to be printed: 2

one more time

one more time

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Program m_and_ns.py

Task

• Individually print out the integers in a user-indicated upward integer interval.

Realizations

• Because the size of the interval is not known when the program is being written, a loop is needed.

• Need a loop that supplies the integers in the interval one-at-a-time.

• The only thing needed to be done with the current integer from the interval is to print it out.

Some program runs

Enter start and end: 2 6

2

3

4

5

6

Enter start and end: 4 7

4

5

6

7

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Program n_and_ms.py — prints a user-specified downward interval of numbers

• Individually print out the integers in a user-indicated downward integer interval.

Realizations

• Because the size of the interval is not known when the program is being written, a loop is needed.

• Need a loop that supplies the integers in the interval one-at-a-time.

• The only thing needed to be done with the current integer from the interval is to print it out.

• Some program runs

Enter start and end: 5 1

5

4

3

2

0

Enter start and end: 12 11

12

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Program inty.py

Task

• Prompt user for a list of space-separated integers

• Split reply into a list of strings

• Produce a new list that is the corresponding list of integers

• Print list of strings

• Print list of integers

Realization

• Function int() can only be applied to one string at a time.

• List of integers will need to be accumulated by processing the numeric strings one at a time.

• For each numeric string it will need to be converted to an integer and added to the list of integers being built

• The list of integers needs to be initalized to an empty list.

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I can smile, see

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Schrödinger's cat

 

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© 2020 Jim Cohoon

Resources from previous semesters are available.