Class 06 – Monday, January 31

Fearlessly we march on — variables and strings

A sign for knowing — what the future asks of us — demands we act now

---

Look both ways

• Back or ahead

---

Agenda

• Some Announcements

• Test 1 will be on Friday, March 18th in-class.

• Test 2 will be on Friday, April 22nd in-class.

• Homework grades: Coming Soon!

• 1 duck per day (per person)

• Q&A

• Advance your chrestomathics abilities

• Casting to a decimal

• String method split()

• Help you better understand how a computer works

• Frame memory built-in functions id() and type()

• Consider assignment subtleties

• Swapping variable values

• Assignment commentary

---

Examples

• Program being_powerful.py

• Gets decimal input

• Program trio.py

• Introduces string method function split()

• Program i_get_around.py

• Shows use of function round()

• Program escaping.py

• Explores the use of Python escape character \ for representing special characters.

• Program who_what_and_where.py

• Shows what Python keeps maintains about your variables

• Program the_old_switcheroo.py

• Considers the subtlety of swapping variable values

• Worksheet

• Homework Program all_consuming.py

• Considers the subtlety of swapping variable values

---

Inquiring minds want to know

• BLS Occupational Outlook Handbook

• BLS Occupational Outlook Handbook: computing and information technology

• Job searching

---

Program being_powerful.py

• Note: Today, we'll be following the same general algorithm:

• GET input from user

• FORMAT input into the type of things you need to solve

• COMPUTE (do the work to solve)

• PRINT the solution.

• Problem

• Prompt and get an integer number (the base for the computation)

• Prompt and get a decimal number (the exponent for the computation)

• Compute the value of the integer to power of the decimal number

• Print the result of the computation

• What the solution offers

• Uses the built-in cast functions int() and float() to convert numeric strings into the numbers they represent.

• Why else is it important

• The program has four parts that can serve as a template for much of our future problem solving.

• Get inputs

• Massage inputs into needed values

• Compute result

• Print result

• Three possible program runs

Enter base (integer): 2

Enter exponent (decimal): 0.5

1.4142135623730951

Enter base (integer): 11

Enter exponent (decimal): 3.14

1861.971509290233

Enter base (integer): 4

Enter exponent (decimal): 0.333

1.5866676863822857

---

Program trio.py

• Problem

• From a single input request determine the three words the user supplies

• Why is it important

• Introduces string method function split()

• Two possible program runs

Enter three words: peace joy friends

Your words

peace

joy

friends

Enter three words: ready or not

Your words

ready

or

not

---

Program i_get_around.py

• What it offers

• Introduces function round()

• Two possible program runs

Enter number: 3.1415926

number: 3.1415926

round( number, 6 ): 3.141593

round( number, 5 ): 3.14159

round( number, 4 ): 3.1416

round( number, 3 ): 3.142

round( number, 2 ): 3.14

round( number, 1 ): 3.1

round( number, 0 ): 3.0

round( number ): 3

Enter number: 2.7182818

number: 2.7182818

round( number, 6 ): 2.718282

round( number, 5 ): 2.71828

round( number, 4 ): 2.7183

round( number, 3 ): 2.718

round( number, 2 ): 2.72

round( number, 1 ): 2.7

round( number, 0 ): 3.0

round( number ): 3

---

Program escaping.py

• Program importance

• Introduces the use of Python escape character \ for representing special characters.

• Program output

a: a b c d

b: "Air quotes" are annoying

c: Hello

 

Goodbye

 

len( a ): x

len( a ): 7

len( b ): 25

---

Program who_what_and_where.py

• Purpose

• Show memory frame information

• Introduce built-in functions id() and type().

• id( n ) identifies where in memory to find n

• type( n ) supplies what type of value is n

• Two possible program runs

Enter integer and decimal: 3 4.159

reply: 3 4.159 <class 'str'> 140400369925360

n: 3 <class 'int'> 9720640

x: 4.159 <class 'float'> 140400370194512

Enter integer and decimal: 8 8.88

reply: 8 8.88 <class 'str'> 139778356653296

n: 8 <class 'int'> 9720800

x: 8.88 <class 'float'> 139778356922448

---

Program the_old_switcheroo.py

• Purpose

• Swap the values of two variables

• Worksheet: suggest you print if off and work through the code by hand

• As miswritten

reply = input( 'Enter two words: ' )

w1, w2 = reply.split()

print( )

print( 'w1 =', w1 )

print( 'w2 =', w2 )

print()

# swap the values of w1 and w2

w1 = w2

w2 = w1

# print results

print( 'After swapping' )

print()

print( 'w1 =', w1 )

print( 'w2 =', w2 )

• A program run — what is wrong?

Enter two words: wahoo wah

w1 = wahoo

w2 = wah

After swapping

w1 = wah

w2 = wah

---

Homework Program all_consuming.py

• Problem

• Develop a program that estimates your annual consumption of a commodity based on how much you consume on a typical weekday and on a typical weekend day.

• Assumptions

• The term week denotes 5 weekdays and 2 weekend days.

• Assume a year is exactly 52 weeks (yes, we know a real year is longer, but we will ignore that in this program).

• User supplied inputs are integers.

• Requirements

• The program first prompts the user for the commodity consumed.

• The program then individually prompts the user for two integer inputs: first, the quantity consumed on a typical weekday, then the quantity consumed on a typical weekend day. These are to be requested using two separate prompts.

• The program uses the inputs to compute and report the estimate of the quantity consumed in a year.

• The quantity output should specify the commodity whose use is being reported.

• Strongly suggested agorithm

• Get input commodity of interest

• Get weekday consumption

• Get weekend day consumption

• Compute weekly consumption

• Compute yearly consumption

• Report yearly consumption

• Three possible program runs

What is something you consume daily? paper napkins

How much consumed on a typical weekday: 6

How much consumed on a typical weekend day: 0

You consume 1560 paper napkins per year.

What is something you consume daily? pretzels

How much consumed on a typical weekday: 0

How much consumed on a typical weekend day: 1

You consume 104 pretzels per year.

What is something you consume daily? jelly beans

How much consumed on a typical weekday: 4

How much consumed on a typical weekend day: 12

You consume 2288 jelly beans per year.

---

To do list

• Homework

• Review class artifacts

• Read about strings: sections 04 and 05

• Read more about strings

• Check out the epistles on Python and problem solving

 

---

🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.