Class 6 – Monday, January 27

Fearlessly we march on — variables and strings

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

I say love is love — For aren't we all just people — Living as we're made

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Look both ways

• Back or ahead

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Agenda

• Help you better model how a computer works

• Consider assignment subtleties

• Continues introduction to the string type str

• Advance your chrestomathics abilities

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Illumination

• Extracts from complimenter.py submissions

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Examples

• Program who_what_and_where.py

• shows what Python keeps track of with variables

• Program the_old_switcheroo.py

• Considers the subltety of swapping variable values

• Worksheet

• Program escaping.py

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

• Program combine_and_multiply.py

• Explores the concatenation operator + and the replication operator * when used with strings.

• Program i_need_water.py

• Explores limits on string building

• Program lickety_strip_and_split.py

• Considers cleaning up and dividing strings

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Enquiring minds want to know

• BLS Occupational Outlook Handbook

• BLS Occupational Outlook Handbook: computing and information technology

• Job searching

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Program who_what_and_where.py

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

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

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

• Three possible program runs

Enter word: dabchick

Enter integer: 1112

Enter decimal: 3.14

w is <class 'str'> and is at 140055893338224 and when printed displays dabchick

si is <class 'str'> and is at 140055893314560 and when printed displays 1112

sd is <class 'str'> and is at 140055893314504 and when printed displays 3.14

i is <class 'int'> and is at 140056017208112 and when printed displays 1112

d is <class 'float'> and is at 140056017236280 and when printed displays 3.14

Enter word: hydroxyzine

Enter integer: 2020

Enter decimal: 1.27

w is <class 'str'> and is at 140664446974064 and when printed displays hydroxyzine

si is <class 'str'> and is at 140664446950400 and when printed displays 2020

sd is <class 'str'> and is at 140664446950344 and when printed displays 1.27

i is a <class 'int'> and is at 140664570843952 and when printed displays 2020

d is a <class 'float'> and is at 140664570872120 and when printed displays 1.27

Enter word: 1112

Enter integer: 1112

Enter decimal: 1112

w is <class 'str'> and is at 140565116193848 and when printed displays 1112

si is <class 'str'> and is at 140565116193904 and when printed displays 1112

sd is <class 'str'> and is at 140565116193792 and when printed displays 1112

i is <class 'int'> and is at 140565240087344 and when printed displays 1112

d is <class 'float'> and is at 140565240115512 and when printed displays 1112.0

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Program the_old_switcheroo.py

• Purpose: swap the values of two variables

• Worksheet

• 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

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Program escaping.py

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

Program output

### print strings

a = hatstall

b = a b

c = a b

d = aren't

e = a

b

### string lengths

len( a ) = 8

len( b ) = 4

len( c ) = 3

len( d ) = 6

len( e ) = 3

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Program combine_and_multiply.py

• Explores the concatenation operator + and the replication operator * when used with strings.

Program output

### operator + performs concatenation

a = fire

b = fighter

a + b = firefighter

### * operator produces repeated concatenation

m = Wahoo-Wah!

n = 3

m * n = Wahoo-Wah!Wahoo-Wah!Wahoo-Wah!

n * m = Wahoo-Wah!Wahoo-Wah!Wahoo-Wah!

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Program i_need_water.py

• Explores limits on string building

water = 'H' + 2 + '0'

print( water )

water = 'H' + str( 2 ) + 'O'

print( water )

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Program lickety_strip_and_split.py

• Explores the string member functions strip() and split().

q = ' Look there is a Blibbering Humdinger '

### mis-attempted stripping

q = ' Look there is a Blibbering Humdinger '

### stripping

q = ' Look there is a Blibbering Humdinger '

s = 'Look there is a Blibbering Humdinger'

### splitting

f = 'bananas $0.69'

c = 'SEAS CS 1112'

bananas costs $0.69 per pound

School: SEAS subject: CS number: 1112

### list making

s1 = ['bananas', '$0.69']

s2 = ['SEAS', 'CS', '1112']

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Program all_consuming.py — due Wednesday January 27

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

• Assumptions

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

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

• User supplied numbers 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.

• 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 normal weekday: 6

How much consumed on a normal weekend day: 0

You consume 1560 paper napkins per year.

What is something you consume daily? pretzels

How much consumed on a normal weekday: 0

How much consumed on a normal weekend day: 1

You consume 104 pretzels per year.

What is something you consume daily? jelly beans

How much consumed on a normal weekday: 4

How much consumed on a normal weekend day: 12

You consume 2288 jelly beans per year.

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To do list

• Homework

• Review class artifacts

• Ensure familarity by reading about Python variables, assignment, and input

• Read about Python string capabilities.

• Check out the epistles on Python and problem solving

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All you need is love — All you need is love — All you need is love, love — Love is all you need.     The Beatles

 

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© 2020 Jim Cohoon

Resources from previous semesters are available.