Starting out with Python - Chapter 2 PPT

8/20/2019 Starting out with Python - Chapter 2 PPT

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Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

STARTING OUT WITH

ythonython

First Edition

by

Tony Gaddis

Chapter 2Input, Processing, and Output


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Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 2-2

2.1 Designing a Program

Concept:

Programs must be carefullydesigned before they are written.During the design process,programmers use tools such aspseudocode and owcharts to

create models of programs.


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The Program Development Cycle•Design the Program

•Write the Code

•Correct Syntax Errors

•Test the Program

•Correct Logic Errors

Figure 2-1 The program development cycle


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More About the Design Process

The rocess o! designing a rogram comrises t"oimortant stes#

1.$nderstand the tas% that the rogram is to er!orm

2.Determine the stes that must be ta%en to er!orm

the tas%


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More About the Design Process

1.$nderstand the tas% that the rogram is toer!orm

a. &nter'ie" the customer

b. De'e(o the software requirement (a simple task that

the program must perform in order to satisfy the ustomer!


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More about the design process

2. Determine the stes that must be ta%en to er!orm

the tas%.

• De'e(o an a(gorithm) a set o! "e((-de!ined (ogica( stes

that must be ta%en in order to er!orm a tas%.

For Exam(e#

Write a rogram to ca(cu(ate and dis(ay the gross ay !or an hour(y

aid em(oyee.

1. Get the number of hours worked.2. Get the hourly pay rate

3. Multiply the number of hours worked by the hourly pay rate.

4. Display the result of the calculation that was performed in step 3.


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Pseudocode is an in!orma( (anguage used to de'e(o a

rogram*s design. &t has no syntax ru(es and is not

meant to be comi(ed or executed.

For Exam(e#

Write a rogram to ca(cu(ate and dis(ay the gross ay !or an hour(y aid

em(oyee.

Input the hours worked

Input the hourly pay rate

alculate !ross pay as hours worked multiplied by hourly pay rateDisplay the !ross pay


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Figure 2-2 Flowchart for the pay

calculatng program

+ !(o"chart is a too( that grahica((y

deicts the stes that ta%e (ace in

a rogram.

Tyes o! Symbo(s#

•,'a(saear at the to or bottom

o! the !(o"chart) and are ca((ed

termina( symbo(s

•Para((e(ogramsused as inut and

outut symbo(s

•ectang(esused as rocessingsymbo(s

•+rro"sreresent the !(o" o! the

rogram


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2.2 &nut) Processing) and ,utut

Concept:

Input is data that the program

receives. When a programreceives data, it usuallyprocesses it by performing someoperation with it. The result ofthe operation is sent out of theprogram as output.


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Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Computer programs perform the following

three steps:

1.&nut is recei'ed

2.Some rocess is er!ormed on the inut

/.,utut is roduced

2.2 &nut) Processing) and ,utut

Figure 2-/ The nput#proce$$ng# and output of

the pay calculatng program

2-1"


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2./ Dis(aying ,utut "ith the print

Statement

Concept:

You use the print statementto display output in a Pythonprogram.


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Statement

Strings and String iterals

• + string is a se0uence o! characters that is used as

data.

• When a string aears in the code o! a rogram) it

is ca((ed a string (itera(.

• &n Python) sing(e-0uotes 3 or doub(e-0uotes 43

can be used to enc(ose string (itera(s.


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Statement

Program 2-/ %apo$trophe&py'


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Statement

Program 2-5 %d$play()uote&py'


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2.5 Comments

Concept:

omments are notes of

e!planations that document linesor sections of a program.omments are part of theprogram, but the Pythoninterpreter ignores them. Theyare intended for people who maybe reading the source code.


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2.5 Comments


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2.6 7ariab(es

Concept:

" variable is a name thatrepresents a value stored in the

computer#s memory.


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Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 12-1!

2.6 7ariab(es

Figure 2-5 The age vara*le

reference$ the value 25


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2.6 7ariab(es

Program 2-8

%vara*le(demo2&py'

Figure 2-6

Two vara*le$


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2.6 7ariab(es


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2.6 7ariab(es


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2.6 7ariab(es

Tab(e 2-1 +ample vara*le name$


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2.6 7ariab(es

Program 2-9 %vara*le(demo3&py'


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2.6 7ariab(es

Program 2-1:%vara*le(demo4&py'

Figure 2-; ,ara*lerea$$gnment n

rogram 2-1"


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2.6 7ariab(es


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2.6 7ariab(es

Program 2-11 %$trng(vara*le&py'


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2.; eading &nut !rom the


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!eading Strings with the raw_input "unction

The raw_input functon retreve$ all .ey*oard nput a$ a

$trng&



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2.= Per!orming Ca(cu(ations

Concept:

Python has numerous operatorsthat can be used to perform

mathematical calculations.


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Tab(e 2-2 ython math operator$


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Program 2-16%$ale(prce&py'


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For Example:num_add = 17 + 5 # the answer will be22num_div_int = 3 2 # the answer is 1! "5is the $ra%tional part # and it is trun%atednum_div_real = 3" 2" # the answer is

15


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1 &perations that are en%losed inparentheses

2 Exponentiation ''3 (ultipli%ation ') division ) and remainder

* ,ddition + and subtra%tion -Tab(e 2-/ +ome e/pre$$on$


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Tab(e 2-5 0ore e/pre$$on$ and ther value$


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The #$ponent and !emainder %perators>> is the exonent oerator. &ts urose is to raise a

number to a o"er.

For Exam(e#

area ? (ength>>2

@ is the remainder oerator. &ts urose is to er!orm

di'ision and return the remainder.

For Exam(e#

(e!to'er ? 1= @ / Aremainder is 2


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Tab(e 2-; lge*rac and programmng e/pre$$on$


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2.8 Bore +bout Data ,utut

Tab(e 2-= +ome of ython$ e$cape character$


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When the is used "ith t"o strings) it er!orms

string concatenation.

For Exam(e#

rint this is* one string.* A one string is aended to another

,utut#

This is one string


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Figure 2-8 $ng the $trng format operator

Program 2-21 %formattng&py'


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Program 2-2/ %column$&py'


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&'#ST(%)S

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Chapter 2Input, Processing, and Output

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Starting out with Python - Chapter 2 PPT