CPSC$231:$ Getting$Started$With$Python$ Programming
Contents
1. eNamed constants What are named constants and how they differ from regular variables What are the benefits of using a named constant vs unnamed constant eWhat are the Python operators for common mathematical operations eHow do the precedence rules order of operation work in Python elnput How to get a program to acquire and store information from the user of the program eWhat is program documentation and what are some common things that are included in program documentation eThe existence of prewritten Python functions and how to find descriptions of them James Tam Copyright Notification e Unless otherwise indicated all images in this presentation are used with permission from Microsoft James Tam2. slide 49 CPSC 231 Getting Started With Python Programming You will learn basic concepts which apply to all Pythons such as getting user input and displaying output Department of Computer Science University of Calgary Fall 2014 Python History e Developed in the early 1990 s by Guido an Rossum ePython was designed with a tradeoff in mind from Python for everyone Horstman and Necaise Pro Python programmers could quickly write programs and not be burdened with an overly cain and proud of i difficult lan guage E AE E Con Python programs weren t optimized to run as efficiently as programs written in some other languages James Tam Working At Home 2 e Alternative continued Requires that Python is configured the path on your computer itis not mandatory to install Python at home follow these instructions carefully missteps occur at your own peril ehttp docs python org using windows html ehttp docs python org using unix html ehttp docs python org using mac html If you have installed Python on your own computer and still can t get Python to run because of the path problems this approach works although it s a inelegant solution eNote where you installed Python folder or directory Create and run your Python programs from this location e It s inelegant because you will eventually have a mess from creating many programs all
3. Displaying Output Using The print Function eThis function takes zero or more arguments inputs Multiple arguments are separated with commas print will display all the arguments followed by a blank line move the cursor down a line end isn t mandatory but can be useful to prevent Python from adding the extra line when precise formatting is needed Zero arguments just displays a blank line eSimple Examples output1 py KN print hey end print sup slide 68 James Tam Displaying Output Using The Print Function 2 Format print argi arg2 1 Example output2 py num 10 0 name james print Sup print Num end print num Exercise remove these and see if you print can correctl print My name name j predict the results Sup Num 10 0 1 From what you ve learned thus far each argument can be a constant string or name of a variable slide 69 James Tam Triple Quoted Output eUsed to format text output free form and to reduce the number of calls to the print function eThe way in which the text is typed into the program is exactly the way in which the text will appear onscreen eProgram name formatting1 pyc VII Il LERLA 4 eee ee TSE a A l H AA From Python Programming 2 4 Edition by Michael Dawson From a CPSC 231 assignment courtesy of James Tam James Tam Formatting Output eO
4. 100 000000 Alarm Causes the program to beep Newline Moves the cursor to beginning of the next line Tab Moves the cursor forward one tab stop Single quote Prints a single quote Double quote Prints a double quote Backslash Prints one backslash 1 Since the question inevitably comes up each term I m answering it now slide 79 James Tam slide 80 James Tam Escape Codes 2 Escape Codes Application eProgram name formatting4 py elt can be used to nicely format text output alignment output provide separators within and between lines print a Beep eProgram example formattings py firstName James Last name print hi nthere LAS NAMES lal First name mobile 123 4567 Pintar UILLGLL print it s TIP print Last name t lastName print First name t firstName print he y you print Contact t 3 mobile eEscape codes for aligning text is even more valuable if the width of a field data to be displayed is variable e g comes from user input or a text file slide 81 James Tam slide 82 James Tam Extra Practice e Traces Modify the examples output using format specifiers and escape codes so that they are still valid Python statements e Alternatively you can try finding some simple ones online or from a textbook Hand trace the code execute on paper without running the program Then run the program and compare t
5. We will talk about other run time errors later James Tam 1 Syntax Translation Errors eEach language has rules about how statements are to be structured eAn English sentence is structured by the grammar of the English language My cat sleeps the sofa Grammatically incorrect FYI missing the preposition to introduce the prepositional phrase the sofa ePython statements are structured by the syntax of Python 5 num Syntactically incorrect the left hand side of an assignment statement cannot be a literal unnamed constant or variable names cannot begin with a number James Tam 1 Some Common Syntax Errors eMiss spelling names of keywords e g primt instead of print eForgetting to match closing quotes or brackets to opening quotes or brackets e g print hello eUsing variables before they ve been named allocated in memory eProgram name error_syntax py raceback most recent call last print num File syntax py line 1 in lt module gt num 123 rint num ameError name num is not defined 2 Runtime Error An Example eProgram name error_runtime py num2 int input Type in a number num3 int input Type in a number num1 num2 num3 When zero is entered for num3 print num1 1 When num3 contains zero slide 128 James Tam 3 Logic Errors eThe program has no syntax errors eThe program runs from begin
6. calories used 10 x weight 6 25 x height 5 x age 161 James Tam Extra Practice eProvide a formula where it would be appropriate to use named constants should be easy eProvide a formula where unnamed constants may be acceptable may be trickier eSearch for formulas in science articles online if you are stuck James Tam Arithmetic Operators Description Example Assignment num 7 Addition num 2 2 Subtraction num 6 4 Multiplication num 5 4 Division num 9 2 num 9 2 Integer division Modulo num 8 3 Exponent num 9 2 slide 95 James Tam Order Of Operation And Style eEven for languages where there are clear rules of precedence e g Java Python it s good style to explicitly parenthesize your operations and use blank spaces as separators x a b c d elt not only makes it easier to read complex formulas but also a good habit for languages where precedence is not always clear e g C C slide 97 James Tam Order Of Operation eFirst level of precedence top to bottom eSecond level of precedence If there are multiple operations that are on the same level then precedence goes from left to right Brackets inner before Example outer Keo 2 3 Exponent Vs xes 3 2 ee 2 Multiplication division modulo Addition subtraction Assignment slide 96 James Tam Input eThe co
7. reference to that a cupsent Population James Tam Why Use Named Constants 2 2 Makes the program easier to maintain If the constant is referred to several times throughout the program changing the value of the constant once will change it throughout the program Using named constants is regarded as good style when writing a computer program James Tam Purpose Of Named Constants 4 PERE ET initialization of the constant changes every reference to that constant BIRTH_RATE 0 998 MORTALITY_RATE 0 1257 populationChange currentPopulation 1000000 populationChange BIRTH_RATE MOR if populationChange gt print Increase print Birth rate BIRTH_RATE MORTALITY_RATE Population chan elif populationChange lt print Decrease print Birth rate BIR MORTALITY_RATE Population else print No change print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange currentPopulation rtality rate populationChange Mortality rate populationChange James Tam When To Use A Named Constant e Rule of thumb If you can assign a descriptive useful self explanatory name to a constant then you probably should eExample 1 easy to provide self explanatory constant name INCH_CM_RATIO 2 54 height height INCH_CM RATIO eExample 2 providing self explanatory names for the constants is difficult
8. eThese numeric values are stored in the computer using binary Character ASCII numeric code Binary code 65 01000001 66 01000010 97 01100001 50 00110010 James Tam Variables Storing Information Optional Details elnformation must be converted into binary to be stored on a computer User enters Can be stored as PPP PPP PD slide 100 James Tam Storing Real Numbers In The Form Of Floating Point Optional Details Sign Mantissa Exponent 1 bit Several Several bits bits Mantissa digits of the number being stored Exponent the direction negative left positive right and the number of places the decimal point must move float when storing the real number as a floating point value eExamples with 5 digits used to represent the mantissa e g One 123 45 is represented as 12345 10 e g Two 0 12 is represented as 12000 10 e g Three 123456 is represented as 12345 10 eRemember Using floating point numbers may result in a loss of accuracy the float is an approximation of the real value to be stored James Tam Storing Information Bottom Line eWhy is it important to know that different types of information is stored differently One motivation sometimes students don t know why it s significant that 123 is not the same as the number 123 Certain operations only apply to certain types of information and can produce errors
9. in the same location James Tam slide 46 slide 48 slide 50 Python eThis is the name of the programming language that will be used to illustrate different programming concepts this semester My examples will be written in Python Your assignments will be written in Python eSome advantages from Python dot org Free Powerful Widely used Google NASA Yahoo Electronic Arts some Linux operating system scripts etc eNamed after a British comedy Monty Python s Flying Circus Official website Python the programming language not the Monty Python comedy troop http www python or An overview of the web site https www python or about gettingstarted James Tam Working At Home eSAFEST APPROACH for working at home recommended Remotely login to the Computer Science network Example Connect using a remote login program such as SSH eInfo htt ages cpsc ucalgary ca tamj 231 startin ssh_index html eDownload http www ucalgary ca it software downloads SSH comes with MacOS so no download is needed e SSH still needs to be installed but it is easier to install SSH than it is to install and setup Python eThere s a learning curve for the interface but it will will be the same in the CPSC lab vs working at home eSometime later in the semester in tutorial the Teaching Assistants will show you how to use this program e Students who took CPSC 101 will have likely learned how to use SSH eAl
10. Be Formatted Via Format Specifiers Placeholder Formatting Effects Using Format Specifiers Format lt width gt 1 lt precision gt 2 lt type of information gt Type of Information to display eExamples format specifiers to format output Program name formatting3 p num 12 55 print 4 1 num print 5 1 num print 3 1 num print 3s 3s ab ab print 3s 3s ab ab String Integer d decimal base 10 Floating point 1 A positive integer will add leading spaces right align negatives will add trailing spaces left align Excluding a value will set the field width to a value large enough to display the output 2 For floating point data only slide 75 James Tam slide 76 James Tam One Application Of Format Specifiers elt can be used to align columns of text eExample movie credits tabular or financial information slide 77 James Tam 1 Escape Codes Characters Percent Sign eThe back slash character enclosed within quotes won t be elf no format specifiers are used then simply enclose the displayed but instead indicates that a formatting escape code within the quotes of a print statement will follow the slash print 12 gt 12 Escape sequence Description elf format specifiers are used within a call to print then use One percent sign to act as an escape code for another percent sign to follow print F 100 gt
11. anguage for writing a program Somewhat analogous to the grammar of a human language If the rules are violated then the typical outcome is the program cannot be translated nor run eA language such as Python may allow for a partial execution it runs until the error is encountered eStyle requirements Approaches for producing a well written program The real life analogy is that something written in a human language may follow the grammar but still be poorly written If style requirements are not followed then the program can still be translated but there may be other problems more on this during the term slide 61 James Tam slide 60 slide 62 The Assignment Operator e The assignment operator used in writing computer programs does not have the same meaning as mathematics Don t mix them up e Example y 3 x y xX 6 y 13 e What is the end result How was this derived what are the intermediate results e See the program assignment py James Tam Variable Naming Conventions 2 1 Style requirement The An name should be T as meaningful 2 Style and Python 2 height yes 2x height no requirement Names must start with a letter Python requirement and should not begin with an underscore style requirement 3 Style requirement Names are case sensitive but avoid distinguishing variable names only by case 3 Name name nAme no to this tri
12. ate run a program you should first navigate to the directory folder where your Python program resides JT the cd command changes your directory Windows and UNIX Suppose my program was under C 231 Windows OR home 231 UNIX To reach this location you could shortcuts excluded for now then type cd c 231 Windows don t type in the brackets or the stuff in between OR cd home 231 UNIX don t type in the brackets or the stuff in between slide 57 James Tam Variables eSet aside a location in memory Used to store information temporary This location can store one piece of information ePutting another piece of information at an existing location overwrites previous information At most the information will be accessible as long as the program runs i e it s temporary eSome types of information which can be stored in variables include integer whole floating point fractional strings essentially any characters you can type and more Format creating lt name of variable gt lt Information to be stored in the variable gt Examples creating Integer e g num1 10 Floating point e g num2 10 0 Strings alpha numeric other characters enclosed in quotes e g name james eTo be safe get in the habit of using double quotes Image curtesy of James Tam slide 59 James Tam Variable Naming Conventions ePython requirements Rules built into the Python l
13. directory sub link http pages cpsc ucalgary ca tamj 231 examples intro home 231 examples intro FYI examples give TA s for tutorials will be in a different location http pages cpsc ucalgary ca tamj 231 tutorialSchedule html home 231 tutorials Creating Running Programs One Operating System eThe process is similar on other platforms OS s the TA s will show you how to do it on the lab computers Linux during tutorials Step 1 Writing your program You need a text editor e g WordPad Notepad to enter the program It can be done using any editor that you want but don t use a word processor e g MS Word and remember to save it as a text file ending with the suffix dot py py File name Document x Rich Text Format RTF v Text Document Text Document MS DOS Format Unicode Text Document Save as type e The machine binary language instructions can now be directly executed by the computer Details in 24 year 10010100 10000100 10000001 901010100 James Tam James Tam Types Of Translators 1 Interpreters e g Python is an interpreted language e Each time the program is run the interpreter translates the program translating a part at a time e f there are any translation errors during the process of interpreting the program the program will stop execution right where the error is encountered 2 Compilers e g C C are compiled
14. docs python org 3 library functions html Note some assignments may have specific instructions which list functions you are allowed to use assume that you cannot use a function unless 1 it s extremely common e g input and output 2 it s explicitly allowed Read the requirements specific to each assignment When in doubt don t use the pre created code either ask or don t use it and write the code yourself If you end up using a pre created function rather than writing the code yourself you could receive no credit slide 122 James Tam Types Of Programming Errors 1 Syntax translation errors 2 Runtime errors 3 Logic errors James Tam 1 Syntax Translation Errors 2 eThe translator checks for these errors when a computer program is translated to machine language James Tam 2 Runtime Errors eOccur as a program is executing running eThe syntax of the language has not been violated each statement follows the rules syntax eDuring execution a serious error is encountered that causes the execution running of the program to cease eWith a language like Python where translation occurs just before execution interpreted the timing of when runtime errors appear won t seem different from a syntax error eBut for languages where translation occurs well before execution compiled the difference will be quite noticeable eA common example of a runtime error is a division by zero error
15. ell check insert images etc lt program statement gt lt program statement gt slide 117 James Tam slide 118 James Tam Inline Documentation Over Documenting A Program eProvided throughout the program eExcept for very small programs documentation should be elt describes in greater detail the specific features of a part of the included program function loop branch group of related statements eHowever it is possible to over document a program e Stating the obvious Documentation Saving documents num num 1 Variable num increased by one save save document under the current name save as rename the document to a new name Documentation can be useful in this case lt program statement gt lastRow SIZE 1 Row numbering begins at zero lt program statement gt Documentation Spell checking The program can spell check documents using the following English variants English British English American English Canadian lt program statement gt lt program statement gt slide 119 James Tam slide 120 James Tam Prewritten Python Functions ePython comes with many functions that are a built in part of the language e g print input elf a program needs to perform a common task e g finding the absolute value of a number then you should first check if the function has already been implemented eFor a list of all prewritten Python functions https
16. gram features have been completed tested and the errors removed debugged a new version should be saved in a separate file Game Oct2 Version Oct 2 2012 Program features 1 Save game Game py Version Oct 2 2012 Program features 1 Save game Version Sept 20 2012 Program features 1 Load game 2 Show game world Version Sept 20 2012 Program features 1 Load game 2 Show game world Game Sept20 Version Sept 20 2012 Program features 1 Load game 2 Show game world James Tam Program Documentation 2 Doesn t contain instructions for the computer to execute eNot translated into machine language eConsists of information for the reader of the program What does the program as a whole do e g calculate taxes What are the specific features of the program e g it calculates personal or small business tax What are it s limitations e g it only follows Canadian tax laws and cannot be used in the US In Canada it doesn t calculate taxes for organizations with yearly gross earnings over 1 billion What is the version of the program elf you don t use numbers for the different versions of your program then simply use dates tie versions with program features more on this in a moment Program versioning and backups James Tam Program Versioning And Back Ups eAs significant prog
17. he actual vs expected result eProgram writing Write a program the will right align text into 3 columns of data Write a program the will left align text into 3 columns of data slide 84 James Tam Reminder Variables Named Constants eBy convention variable names are all lower case eThey are similar to variables a memory location that s been eThe exception is long multi word names given a name ee eUnlike variables their contents shouldn t change e As the name implies their contents can change as a program runs e g assume interest and bonuses are set to valid values income 300000 income income interest Income income bonuses eExample PI 3 14 PI Named constant 3 14 Unnamed constant eThe naming conventions for choosing variable names generally apply to constants but the name of constants should be all UPPER CASE You can separate multiple words with an underscore eThey are capitalized so the reader of the program can distinguish them from variables For some programming languages the translator will enforce the unchanging nature of the constant i e giving it a new value is an error For languages such as Python it is up to the programmer to recognize a named constant and not to change it slide 85 James Tam slide 86 James Tam Why Use Named Constants 1 They make your program easier to read and understand NO populationChange 0 1758 0 1257 currentPopulatio
18. languages e Before the program is run the compiler translates the program all at once e f there are any translation errors during the compilation process no machine language executable will be produced nothing to execute e f there are no translation errors during compilation then a machine language program e g exe files is created which can then be executed James Tam The First Python Program eProgram name small py Filename small py print hello end James Tam Creating Running Programs One Operating System 2 Step 2 Translating and running your program You need to open a command line to translate run your Python program The name of the Python translator is Python Type the name of a program folder document or Internet resource and Windows will open it for you Log Off tamj Open Earl v Shut Down Lox Cancel Browse To translate run your program type python filename py at the command line e The first example program would be executed by typing python small py e For a program whose filename is called output1 py you would type python output1 py Windows XP James Tam Important Reminders e Make sure you type the whole file name including the part after the period when you translate run your program E g python small py e Unless you are very familiar with your operating system when you transl
19. mation Getting Numeric Input eThe input function only returns string information so the value returned must be converted to the appropriate type as needed Example Program name convert3 py No conversion performed problem HUMAN_CAT_AGE_RATIO 7 age input What is your age in years Age refers to a string catAge age HUMAN_CAT_AGE_RATIO not a number print Age in cat years catAge s The te nse mathematical multiplication slide 108 James Tam Program Documentation eProgram documentation Used to provide information about a computer program to another programmer writes or modifies the program eThis is different from a user manual which is written for people who will use the program Documentation is written inside the same file as the computer program when you see the computer program you can see the documentation eThe purpose is to help other programmers understand the program what the different parts of the program do what are some of it s limitations etc James Tam Program Documentation 3 eFormat lt Documentation gt The number sign flags the translator that the remainder of the line is documentation eExamples Tax It v1 0 This program will electronically calculate your tax return This program will only allow you to complete a Canadian tax return James Tam Program Versioning And Back Ups eAs significant pro
20. mputer program getting string information from the user eStrings cannot be used for calculations information for getting numeric input will provided shortly Format lt variable name gt input OR lt variable name gt input lt Prompting message gt Avoid alignment issues such as this eExample Program name input1 py print What is your name name input OR name input What is your name OR print What is your name end name input our name your name foo slide 98 James Tam Variables Storing Information Optional Details eOn the computer all information is stored in binary 2 states Example RAM memory stores information in a series of on off combinations A single off off combination is referred to as a bit Bit slide 99 James Tam Storing Integer Information Optional Details e1 bit is used to represent the sign the rest is used to store the size of the number Sign bit 1 on negative 0 off positive Format Positiv a number 4 1 bit Digits representing the size of the number all the remaining bits aie P number ePrevious example T Size of number in this case Positive 13 number i P PPPPPPP WSN James Tam Storing Character Information Optional Details eTypically characters are encoded using ASCII eEach character is mapped to a numeric value E g A 65 B 66 a 97 2 50
21. n ee Vs Avoid unnamed constants whenever possible YES BIRTH_RATE 17 58 MORTALITY_RATE 0 1257 currentPopulation 1000000 populationChange BIRTH_RATE MORTALITY_RATE currentPopulation Purpose Of Named Constants 3 BIRTH_RATE 9 998 MORTALITY_RATE 9 1257 populationChange currentPopulation 1000000 James Tam populationChange BIRTH_RATE MORTALITY_RATE currentPopulation if populationChange gt print Increase print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange elif populationChange lt print Decrease print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange else print No change print Birth rate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange Purpose Of Named Constants 5 BIRTH RATE 9 1758 MORTALITY_RATE 0 0001 populationChange currentPopulation 1000000 populationChange BIRTH_RATE MORTAL if populationChange gt print Increase print Birth ra ortality rate populationChange H_RATE Mortality rate MORTALITY_RATE populationChange else print No chan print Birt ate BIRTH_RATE Mortality rate MORTALITY_RATE Population change populationChange James Tam One change in the initialization of the onstant changes every
22. ning to end with no runtime errors eBut the logic of the program is incorrect it doesn t do what it s Some Additional Examples Of Errors eAll are external links not produced by your instructor http levellwiki wikidot com syntax error http www cs bu edu courses cs108 guides debug html http cscircles cemc uwaterloo ca 1e errors http www greenteapress com thinkpython thinkCSpy html app01 html supposed to and may produce an incorrect result eProgram name error_logic py print This program will calculate the area of a rectangle length int input Enter the length width int input Enter the width area length width print Area area slide 129 James Tam slide 130 James Tam Practice Exercise e This one will be an ongoing task eAs you write you programs classify the type of errors that you encounter as syntax translation runtime or logical slide 131 James Tam Layout And Formatting Layout And Formatting Example Creating reference to grid eSimilar to written text all computer programs except for the aGrid smallest ones should use white space to group related instructions and to separate different groups These are output statements to prompt for user information Creating the grid data for r in range 0 2 1 Instruction1 aGrid append Instruction2 for c in range 0 3 1 Instruction3 aGrid r append str rtc Instruction4 Di
23. o James Tam Variable Naming Conventions 2 Key Words In Python 4 Style requirement Variable oo names should generally be all age height weight yes and as assert break lower case see next point for Age HEIGHT no class continue def del the exception elif else except exec 5 Style requirement For names m composed of multiple words poe eee E anne finally for From global spparalg each word by yes to either approach if import in s capitalizing the first letter of lambda not o pass each word save for the first word or by using an underscore print ralse return try Either approach is acceptable but don t mix and match 6 Python requirement Can t be a keyword see next slide Pe ae 1 From Starting out with Python by Tony Gaddis renee Variable Naming Conventions Bottom Line Extra Practice eBoth Python and style requirements should be followed eTraces when creating your variables Modify the examples output using format specifiers and escape codes so that they are still valid Python statements e Alternatively you can try finding some simple ones online or from a textbook Hand trace the code execute on paper without running the program Then run the program and compare the actual vs expected result eProgram writing Write a program the will right align text into 3 columns of data Write a program the will left align text into 3 columns of data slide 65 James Tam slide 84 James Tam
24. or unexpected results when applied to other types of information eExample num input Enter a number numHalved num 2 James Tam Converting Between Different Types Of Information eExample motivation you may want numerical information to be stored as a String for built in string functions e g check if a string consists only of numbers but also you want to perform calculations eSome of the conversion mechanisms functions available in Python Value to convert Format int lt value to convert gt float lt value to convert gt str lt value to convert gt Examples Program name convert1 py x 10 9 y int x print x y slide 105 James Tam Converting Types Extra Practice eDetermine the output of the following program print 12 33 print 12 33 xX 12 y 21 print x y print str x str y slide 107 James Tam Converting Between Different Types Of Information Getting Numeric Input 2 Input converted Problem solved HUMAN_CAT_AGE_RATIO 7 age int input What is your age in years i acaba catAge age HUMAN_CAT_AGE_RATIO a print Age in cat years catAge The now multiplies a numeric value slide 109 James Tam Converting Between Different Types Of Information 2 Examples Program name convert2 py x 100 y 10 5 print x y print int x float y slide 106 James Tam Converting Between Different Types Of Infor
25. ram features have been completed tested and the errors removed debugged a new version should be saved in a separate file Game py Game Sept20 Version Sept 20 2012 Program features 1 Load game 2 Show game world ake backup file Version Sept 20 2012 Program features 1 Load game 2 Show game world James Tam Backing Up Your Work eDo this every time that you have completed a significant milestone in your program What is significant will vary between people but make sure you do this periodically eldeally the backup file should be stored in a separate directory folder better yet on a separate device and or using an online method such as an email attachment or cloud storage eCommon student reason for not making copies Backing up files takes time eCompare Time to copy a file 10 seconds generous in some cases Time to re write your program to implement the feature again 10 minutes might be overly conservative in some cases Failing to backup your work is not a sufficient reason for receiving an extension James Tam Types Of Documentation Header Documentation eHeader documentation eProvided at the beginning of the program elnline documentation elt describes in a high level fashion the features of the program as a whole major features without a great deal of detail HEADER DOCUMENTATION Word Processor features print save sp
26. splaying the grid for r in range 0 2 1 for c in range 0 3 1 sys stdout write str aGrid r c print These are instructions to perform calculations on the user input and display the results Instruction5 Instruction6 slide 133 James Tam slide 134 James Tam Section Summary Layout And Formatting eWhy is layout and formatting of programs important how to do it James Tam After This Section You Should Now Know eHow to create translate and run Python programs eVariables What they are used for How to access and change the value of a variable Conventions for naming variables How information is stored differently with different types of variables converting between types eOutput How to display messages that are a constant string or the value stored ina memory location variable or constant onscreen with print eHow why to use triple quoted output eHow to format output through The use of format specifiers Escape codes James Tam After This Section You Should Now Know 3 eWhat are the three programming errors when do they occur and what is the difference between each one eHow to use formatting to improve the readability of your program James Tam Extra In Case You re Interested Different languages may have unique style guides eHere is the style guide for Python http legacy python org dev peps pep 0008 James Tam After This Section You Should Now Know 2
27. ternative not recommended Getting Python if you do this make sure you get version 3 X and not version 2 X http www python org download James Tam Online Help Official Python Site e Basic explanation of concepts for beginners along with examples to illustrate http docs python org py3k tutorial index htm You may want to skip Step 1 and proceed immediately onto Step 2 1 and continue onto Step 3 James Tam Slide 53 slide 55 Translation Aspecial computer program translator translates the program written by the programmer into the only form that the computer can understand machine language binary Program Creation e A person programmer writes a computer program series of instructions oo Execution e The program is written and saved using a text editor e The instructions in the programming language e g Python are high level look much like a human language Details later this term list 1 2 a 10000001 for element in list print element Images curtesy of James Tam Location Of My Online Examples eFinding them via the WWW URL http pages cpsc ucalgary ca tamj 231 examples eFinding them in UNIX when you are logged onto a computer in the lab or remotely logged in using SSH Directory nhome 231 examples eThe locations of the example programs that are specific to this section of notes each section will have be located in a sub
28. utput can be formatted in Python through the use of format specifiers and escape codes James Tam Print Vs Print lt name gt eEnclosing the value in parentheses with quotes means the value in between the quotes will be literally displayed onscreen eExcluding the quotes will display the contents of a memory location eExample output3 py aString Some message print aString Some message print aString aString James Tam By Default Output Is Unformatted eExample num 1 3 print num num ry J s 3333333333333333 num Sometimes you get extra spaces or blank lines The number of places of precision is determined by the language not the programmer e There may be other issues e g you want to display output in columns of fixed width or right left aligned output e There may be times that specific precision is needed in the displaying of floating point values slide 72 James Tam Format Specifiers eFormat print lt type of info to display code gt lt source of the info to dispLlay gt Doesn t literally display this Placeholder for information to be displayed eExample starting with simple cases Program name formatting2 py num 123 st cpsc 231 print num d num print course s st num 1273 num 12 5 print F d num num cpsc 231 course 1 2 Snnnnn 1 2 James Tam Types Of Information That Can
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