03 - Introduction to Programs and Python

8/20/2019 03 - Introduction to Programs and Python

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Introduction to Programs andPython

Introductory Computing


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Computers want to be helpful...

• Computers are b uilt for one p urpose - t o dothings f or us

• But we need to speak t heir language todescribe what we want done

• Users have i t easy - s omeone already p utmany d ifferent programs ( instructions) intothe computer and users just pick t he oneswe want to use

WhatNext?

WhatNext?

WhatNext?

WhatNext?


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Programmers AnticipateNeeds

• iPhone Applications ar e a market

• iPhone Applications h ave over 3 Billiondownloads

• Programmers h ave left their jobs t o befull-time iPhone developers

• Programmers know the ways of theprogram

PickMe!

PickMe!

PickMe!

PickMe!


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Users vs. Programmers

• Users s ee computers as a s et of tools - word processor, spreadsheet, map,todo list, etc.

• Programmers learn the computer “ways ” an d the computer language

• Programmers have s ome t ools that allow them to build new tools

• Programmers s ometimes w rite tools f or lots of users and sometimesprogrammers w rite little “helpers ” for themselves to automate a task


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ComputerHardware + Software

Networks....From a software creator ’s point of view, we build the software.

The end users (stakeholders actors! are our masters " who wewant to please " often the# pa# us mone# when the# are pleased.$ut the data, information, and networks are our problem to solveon their behalf. The hardware and software are our friends and

allies in this %uest.

&nformation'ata

User

ogram


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Why learn to code?Programming is a p owerful tool you can use to solve all kinds ofproblems

• What do you want to do?

Build a p hone app to help you find directions

Calculate how much m oney you n eed t o buy a c ar

See what people are saying a bout your business on socialmedia

Program a wearable d evice so i t tweets you when youshould re-apply sunscreen


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Why be a programmer?

• To get some t ask done - we are t he u ser and programmer

> Clean up survey d ata

•To produce something for others to use - a p rogramming job> Fix a p erformance p roblem in the Sakai software

> Add guestbook to a w eb site


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h# )#thon*

There are a T of di-erent pro rammin lan ua es out there

)#thon is one of the easier ones to learn

There are lots of free tools out there #ou can use to code or learn)#thon

There are a lot of di-erent wa#s to use )#thon code


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/nd as a bonus

nce #ou learn how to code in one pro rammin lan ua e it will be easier to learn anotherpro rammin lan ua e, and another, and another0

C1

2avaScript

C++

)erl

***


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$ut let3s be clear about somethin 0

4ou won3t learn enou h in this course to start addin special e-ects tothe ne5t bi superhero movie

4ou & learn enou h to start solvin real world problems with code

6 to 7ust start havin some fun


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So how do & et started*


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How do & know & installed ever#thincorrectl#*

There is a tradition amonpro rammers

e alwa#s test our installation b#writin the same pro ram8

Hello o


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Creating your Hello World program!


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You have now created your first applicationprint( 'Hello World'

)


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Congratulations you are now a coder


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What is Code? Software?A Program?

• a seq uence of instructions t hat specifies ho w to perform a co mputation

> It is a little piece of our intelligence in the computer

> It is a little piece of our intelligence we can give to others - w e figuresomething o ut and then we e ncode i t and then give i t to someone e lse t osave them the time and energy of figuring it out

• A piece of creative art - p articularly when we do a g ood job on userexperience


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Some basic i nstructions•input : data you type a te t you load

•output : display data on the screen send data to a file

•math : perform "asic mathematical operations li#e $ % & :

•conditional e ecution : chec# for certain conditions ande ecute the appropriate instructions

•repetition : perform some action repeatedly usually withsome variation

'rogramming ( "rea#ing a large comple tas# into smallerand smaller su"tas#s until the su"tas#s are simple enoughto "e performed with one of these "asic instructions


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Python as a Language


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http:// harrypotter.wikia.com/wiki/Parseltongue

Parseltongue is t he language of serpents an dthose who can converse with them. Anindividual who can speak Parseltongue is

known as a Parselmouth . It i s a veryuncommon skill, and may b e h ereditary.

Nearly all known Parselmouths are d escendedfrom Salazar Slytherin .

http://harrypotter.wikia.com/wiki/Salazar_Slytherinhttp://harrypotter.wikia.com/wiki/Salazar_Slytherin


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Python is the language of the PythonInterpreter and those who can converse with it.An individual who can speak Python is knownas a Pythonista . It is a v ery uncommon skill,

and may b e h ereditary. Nearly a ll known

Pythonistas u se software initially developed by Guido van Rossum .


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Compilers and Interpreters• Two kinds of programs process high-level languages into low-level

languages : interpreters and compilers .

• An interpreter reads a h igh-level program and executes i t, meaning that itdoes w hat the program says. It processes t he program a l ittle at a t ime,

alternately reading lines an d performing computations.


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Compilers and Interpreters• Acompiler reads the p rogram and translates it completely b efore t he

program starts r unning.

• In this ca se, the high-level program is ca lled the source cod e , and thetranslated program is cal led the object code or the executable .

• Once a program is compiled , you can execute it repeatedly without furthertranslation.


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Early Learner: Syntax Errors• We n eed to learn t he Python language so we can communicate our instructions

to Python. I n the b eginning w e w ill make l ots of mistakes an d speak g ibberish l ikesmall children.

• When you m ake a m istake, the computer does not think you are “cute“syntax e rror ” - gi ven that it *knows* t he language and you are just learning it. I tseems l ike P ython is cr uel and unfeeling.

• You must remember that *you* are intesimple and very fast - b ut cannot learn - s o it is ea sier for you to learn Pythonthan for the computer to learn English ...


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Early Learner: Debugging• Programming is a c omplex p rocess, and because i t is done b y h uman beings, it

often leads t o errors. For whimsical reasons, programming errors ar e calledand the p rocess of tracking t hem down and correcting t hem is called bng

•)hree #inds of "ugs:

•synta errors % means that you have violated the “grammar” rules of

'ython•runtime errors % do not appear until after the program has started to ru

•semantic errors % program will run perfectly "ut it will not produceresults you wanted: the meaning of the program *semantics+ is wrong


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csev$ pythonPython 2.5 (r25:51918, Sep 19 2006, 08:49:13)[GCC 4.0.1 (Apple Computer, Inc. build 5341)] on darwinType "help", "copyright", "credits" o r "license" f or moreinformation.>>>

What next?


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csev$ pythonPython 2.5 (r25:51918, Sep 19 2006, 08:49:13)[GCC 4.0.1 (Apple Computer, Inc. build 5341)] on darwinType "help", "copyright", "credits" o r "license" f or moreinformation.>>> x = 1>>> print x1>>> x = x + 1>>> p rint x2>>> exit()

This is a g ood test to make sur e that you havePython correctly installed. Note t hat quit()also works t o end the interactive session.


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Let’s T alk to Python...


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Elements of Python

• Vocabulary / W ords - Variables and Reserved words (Chapter 2)

•Sentence st ructure - va lid syntax patterns (Chapters 3 -5)

• Story st ructure - constructing a p rogram for a p urpose


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Reserved Words

• You can not use reserved words a s va riable names / identifiers

and del for is raise assert elif from

lambda return break else globalnot try class except if or whilecontinue exec import pass yield

def nally in print as with :


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Sentences or Lines

x = 2x = x + 2print x

Variable Operator Constant Reserved Word

Assignment statementAssignment with expression

Print statement


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Programming Paragraphs


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Python Scripts

• Interactive Python is go od for experiments an d programs of 3-4 lineslong

• Most programs are m uch longer, so we type t hem into a f ile a nd tellPython to run the commands in the file

• In a s ense w e ar e “giving Python a scr ipt ”

• As a convention, we ad d “.py ” as t he suffix o n the end of these files t oindicate they contain Python


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Writing a Simple Program


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Interactive versus S cript

• Interactive> You type directly to Python

• Script> You enter a sequence of statments and tell Python to execute the statements i n the file


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Program Steps or Program Flow

• Like a r ecipe or installation instructions, a p rogram is a se quence ofsteps to be d one in order

• Some st eps are conditional - they may b e skipped

• Sometimes a s tep or group of steps are t o be r epeated• Sometimes w e st ore a set of steps to be u sed over and over as

needed several places t hroughout the program (Chapter 4)


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Sequential Steps

Program:

x = 2print xx = x + 2print x

Output:

24

x = 2

print x

x = x + 2

print x

When a p rogram is running, it flows from one st ep to the n ext.As programmers, we set up “paths ” for the program to follow.


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Conditional Steps

Program:

x = 5if x < 10: print ' Smaller’

if x > 20: print ' Bigger'

print ' Finis'

x = 5

x < 10 ?

print 'Smaller'

x > 20 ?

print 'Bigger'

print ' Finis'

Yes

No


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Repeated StepsProgram:

n = 5while n > 0 : print n n = n – 1

print 'Blasto ff!'

n > 0 ?

Loops (repeated steps) have iteration variableschange e ach t ime t hrough a loop. Often these

iteration variables go t hrough a sequence o f numbers.

No

print ' Blasto ff'

Chapter 5

Yes

n = 5

print n

n = n -1


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,c#nowledgements - Contri"utions


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03 - Introduction to Programs and Python

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