Class 4 – Wednesday, January 23

Variation on a theme

A variable — Is like a box or a name — We must all know this

That Black Lives Matter — Should be so easy to grasp — People are people

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Look both ways

• Back or ahead

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What is happening today

• Make sure everyone knows how to print something

• Want you to have a mental model of how to step through code.

• Become reactive

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Download right now

• truth.py

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Download as soon as you can

• variety.py

• hip_hopping_down_the_bunny_trail.py

• echo.py

• favorite_word.py

• psychoanalyst.py

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A code walk through — getting a mental model of variables and assignment

• Slides

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In-class comportment

• If you see that your neighbor is having difficulty with the current task, please ask if you can help

• If you are having difficulty, please ask your neighbor for advice.

• If more is needed, please raise your hand so that the Teaching Assistant can work with you.

• Do not let things stay muddy, you are paying tuition — make use of the assistance that we can provide.

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Agenda

• Further expand our communication skills

• Consider abstraction

• Expand our understanding of variables

• Introduce assignment

• Introduce input acquisition

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Important questions

• What is a variable?

• Why is assignment so important

• Does the old value of a variable hang around for us to use?

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Program variety.py

• Problem

• Perform several assignment statements including an update of a variable.

• What the solution offers

• Basic understanding of variables and assignment.

• The ability to update is crucial when problem solving.

• Check out afterclass

• Epistle

• Different walkthrough

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Program hip_hopping_down_the_bunny_trail.py

• Problem

• Simulate the number of rabbits occurring over five generations.

• What the solution offers

• Examines some nuances of the assignment operator.

• The final version of the program updates the value of variables in terms of themselves; ie., number of rabbits doubles each generation and the generation number is an increment of the previous generation value.

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Program echo.py

• Problem

• Prompt, get, and echo text from the user

• Prompt, get, and echo more text from the user

• What the solution offers

• Introduces built-in function input(). When the function is invoked, its argument is printed to the display, the entry supplied by the user in response to that message is the value of the invocation. The input() function always returns the user reply as a string.

• The input() function allows programs to be interactive; i.e., their actions can be influenced by the user. The input() function enables Python to do general problem solving.

• Three possible program runs

Please provide text: My favorite color is sometimes electric blue

Your reply was: My favorite color is sometimes electric blue

Please provide more text: I know someone whose favorite number is 88

Your new reply was: I know someone whose favorite number is 88

Please provide text: The name Hannah is a palindrome

Your reply was: The name Hannah is a palindrome

Please provide more text: I sometimes misspell misspell as "mispell"

Your new reply was: I sometimes misspell misspell as "mispell"

Please provide text: I like the word dabchicks

Your reply was: I like the word dabchicks

 

Please provide more text: Do you know why I like the word dabchicks

Your new reply was: Do you know why I like the word dabchicks

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Program favorite_word.py

• Problem

• Prompt and get a word of interest from user user

• Compute the length of the word

• Output a message about the length of the word

• What the solution offers

Another use of the built-in function input().

Introduces the built-in function len().

• Three possible program runs

Tell me a favorite word: rhythms

 

Did you know that rhythms has length 7

Tell me a favorite word: strengths

 

Did you know that strengths has length 9

Tell me a favorite word: squirreled

 

Did you know that squirreled has length 10

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Program psychoanalyst.py

• Problem

• Prompt and get what is on the user’s mind

• Prompt and get why the first reply is on their mind.

• Print an out of time message

• What the solution offers

• Introduces the str type operator +. The + operator when evaluated with two strings as its operands, produces as its value, their concatenation.

• Another use of the built-in function input().

• Creates and uses an input prompt that makes use of a prior input.

• Three possible program runs

Tell me what is on your mind: I worry about the future

 

Hmmm. Why is -- I worry about the future -- on your mind: Because it it coming

 

Oh? I wish we had more time to chat. So long.

Tell me what is on your mind: A fluttering butterfly

 

Hmmm. Why is -- A fluttering butterfly -- on your mind: I do not want rain

 

Oh? I wish we had more time to chat. So long.

Tell me what is on your mind: Is superman colorblind

 

Hmmm. Why is -- Is superman colorblind -- on your mind: To account for fashion sense

 

Oh? I wish we had more time to chat. So long.

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To do list

• Review class artifacts

• Ensure familarity with Python variables, assignment, and input

• Look over the Python string module (library)

• Read the epistle on variety.py

• Re-examine the walkthrough

• Look over another walkthrough

• Read, but do not do, the next assignment

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© 2020 Jim Cohoon

Resources from previous semesters are available.