Class 20 – Friday March 1

Control, control

Think before I act — My problem solving mantra — Make it your also

Otto Warmbier — Your life was stolen from you — Is what we believe

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Look both ways

• Back or ahead

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Agenda

• Gain familiarity with decision and iteration control constructs

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Datasets

• Word lists

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Problem who_is_the_longest_of_them_all.py

• Determine the longest word in user text. A constraint on your solution is that the only permitted list is the list of input words.

• Human being-based solution strategy — scan through the words one-at-a-time and determine whether the current word is the longest word so far.

Three possible program runs

Enter text: Otto Warmbier — Your life was stolen from you — Is what I believe

Warmbier

Enter text: Think before I act — My problem solving mantra — Make it your also

problem

Enter text:

problem

Brainstorming

• Because we do not know the number of words to be given when we are writing our solution, we definitely need a loop that can iterate over the list of input words.

• When we process a word we need to be able to determine whether it is in contention for being the longest word.

• If it is the longest word we seen so far, then we need to remember it in order to compare it to the remaining words.

• If it is not the longest word we seen so far, we take no further interest in it.

• For such loop processing to work, we need an accumulator variable keeping track of the longest word found so far. There are two obvious candidates for initializing that variable — making it the empty string or making it the first word. Either can work and there are good arguments for both of them.

• One thing for sure, the variable keeping track of the longest word so far needs to be initialized before the loop — during the loop we are updating it.

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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.`

• Human being-based solution strategy — scan through the text of interest and determine whether current word is not in the correct-spelling word list.

Three possible program runs

Enter text: It was the best of times It was the wurst of times It was October Fest

wurst

fest

Enter text: how much wod can a woodchuck chuck

wod

woodchuck

Enter text:

problem

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 its 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 try to interleaving 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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To do list

• Really examine the above and the artifacts

• Homework 17 due Tuesday. Submissions will be turned on on Monday.