Class 20 — Friday March 4

"if" and "else" and Range

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Look both ways

• Back and ahead

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Agenda

• Being logical

• if statement

• else keyword

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Downloads

• Program robotomy.py

• Program spell_check.py

• Program arrangements.py

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To do

• Review artifacts and/or course recordings on Collab

• Read epistle on decision making

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Problem robotomy.py

• Task — determine what happens when a robot comes knocking on a door

• If the door is locked, the robot should be instructed to turn around.

• If the door is instead unlocked, the robot should be instructed to open the door and enter the room. Before entering, the robot should determine whether the light is off. If it is off, the robot should be instructed to first turn on the light.

• Observations

• There is one procedure to perform if the door is locked, another to perform if it is unlocked

• The procedure to perform if the door is unlocked, requires analysis whether the light is on.

• Some program runs

Door (locked / unlocked): locked

Turn around

Door (locked / unlocked): Unlocked

Open the door

Light (on / off): on

Enter the room

Door (locked / unlocked): unlocked

Open the door

Light (on / off): Off

Turn on the light

Enter the room

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Problem spell_check.py

• Determine misspelled words in user text. To support this activity, there is a GitHub-acquired web file with the 10,000 most commonly used English words on the webs. For those interested, a more-complete list of 173,541 English words is available.

• WWAHD (what would a human do) strategy — scan through the user text and determine whether the current word is not in the correct-spelling word list.

• Some program runs

Enter text: It was the beste of times It was the wurst of times It was Oktoberfest

beste

wurst

oktoberfest

Enter text: how much wod can a woodchuck chuck

wod

woodchuck

Enter text: to be or not to be that is the question

Enter text:

• Brainstorming

• To accomplish the task there are two streams of information to process.

• One stream is the input text; the other stream is the list of word spellings. Processing these streams requires different actions, so we need to be sure when we read from a stream, that we pick the right one.

• To make a decision on a word, we need to know if it’s in the list of correctly-spelled words. This fact tell us that we should get the list of word spellings before we get the user text — it would not really help to get the words first, and it would be a real mess to interleave the stream reading.

• Together, the above tell us a plan of action.

• Import our url module.

• Specify the URL for the spelling dictionary.

• Read the contents of the URL and store it as a list of word spellings.

• Get the user text and convert it into a list of words.

• For each user word, determine whether it is correctly spelled. If it is incorrectly spelled, print it out.

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Decision making

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Problem arrangements.py

• Fun fact: a range is a type of sequence. Other sequences we have used have been strings and lists.

• Up to now whenever we have had a range() loop, we always had two arguments handed to range(). range() can also handle having one or three arguments.

• If a single argument n is given to range(), then Python treats it as range( 0, n ).

• If three arguments are given to range() as in range( m, n, k ), then

• If k is positive, then

• The start value is m; the stop value is less than n; and the other values go up in steps of k

• If k is negative, then

• The start value is m; the stop value is greater than n; and the other values go down in steps of k

• Another fun fact: we can a range sequence into a list sequence using the built-in function list() on a range.

• Some program runs

Enter integers m, n, and k: 3 8 2

i: 3

i: 5

i: 7

list( range( m, n, k ) ): [3, 5, 7]

Enter integers m, n, and k: 10 6 -3

i: 10

i: 7

list( range( m, n, k ) ): [10, 7]

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🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.