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PROGRAM IN PYTHON - PART 123456789greg@earth: /python examples Well, that seems to haveworked, but why does it countup to only 9 and then stop.Look at the output again. Thereare 10 numbers printed,starting with 0 and ending with9. That's what we asked it todo -- print the value of cntr 10times, adding one to thevariable each time, and quit assoon as the value is 10.Now you can see that, whileprogramming can be simple, itcan also be complex, and youhave to be sure of what youask the system to do. If youchanged the range statementto be "range(1,10)", it wouldstart counting at 1, but end at9, since as soon as cntr is 10,the loop quits. So to get it toprint "1,2,3,4,5,6,7,8,9,10", weshould use range(1,11) - sincethe for loop quits as soon asthe upper range number isreached.Also notice the syntax of thestatement. It is "for variable inrange(start value,end value):"The ":" says, we are starting ablock of code below thatshould be indented. It is veryimportant that you rememberthe colon ":", and to indent thecode until the block is finished.If we modified our programto be like this:#! /usr/bin/env pythonfor cntr in range(1,11):indentation shows the blockformatting. We will get intomore block indentationthoughts in our next tutorial.That's about all for thistime. Next time we'll recap andmove forward with morepython programminginstructions. In the meantime,you might want to considerinstalling a python specificeditor like Dr. Python, or SPE(Stani's Python Editor), both ofwhich are available throughSynaptic.print cntrprint 'All Done'We would get an output of.greg@earth: /python examples ./for loop.py12345678910All Donegreg@earth: /python examples Make sure your indentationis correct. Remember,full circle magazine #27is owner of,aconsulting company in Aurora,Colorado, and has beenprogramming since 1972. Heenjoys cooking, hiking, music,and spending time with hisfamily.10contents

HOW-TOIn the last installment, welooked at a simpleprogram using raw inputto get a response from theuser, some simple variabletypes, and a simple loop usingthe "for" statement. In thisinstallment, we will delve moreinto variables, and write a fewmore programs.FCM#27 - Python Part 1DevCD/DVDProgram In Python - Part 2Graphics Internet M/media SystemHDDUSB Drive LaptopWirelessI received an email from DavidTurner who suggested that usingthe Tab-key for indentation of codeis somewhat misleading as someeditors may use more, or less, thanfour spaces per indent. This iscorrect. Many Python programmers(myself included) save time bysetting the tab key in their editor tofour spaces. The problem is,however, that someone else'seditor may not have the samesetting as yours, which could leadto ugly code and other problems.So, get into the habit of usingspaces rather than the Tab-key.Let's look at another type ofvariable called lists. In otherlanguages, a list would beconsidered an array. Goingback to the analogy of shoeboxes, an array (or list) wouldbe a number of boxes all gluedside-by-side holding like items.For example, we could storeforks in one box, knives inanother, and spoons inanother. Let's look at a simplelist. An easy one to picturewould be a list of monthnames. We would code it likethis.months Sep','Ocfull circle magazine #28t','Nov','Dec']To create the list, we bracketall the values with squarebrackets ( '[' and ']' ). We havenamed our list 'months'. To useit, we would say something likeprint months[0] or months[1](which would print 'Jan' or'Feb'). Remember that wealways count from zero. To findthe length of the list, we canuse:print len(months)which returns 12.Another example of a listwould be categories in acookbook. For example.categories ['Maindish','Meat','Fish','Soup','Cookies']Then categories[0] would be'Main dish', and categories[4]would be 'Cookies'. Prettysimple again. I'm sure you canthink of many things that youcan use a list for.7Up to now, we have createda list using strings as theinformation. You can alsocreate a list using integers.Looking back at our monthslist, we could create a listcontaining the number of daysin each one:DaysInMonth [31,28,31,30,31,30,31,31,30,31,30,31]If we were to printDaysInMonth[1] (for February)we would get back 28, which isan integer. Notice that I madethe list name DaysInMonth.Just as easily, I could haveused 'daysinmonth' or just 'X'.but that is not quite so easy toread. Good programmingpractices suggest (and this issubject to interpretation) thatthe variable names are easy tounderstand. We'll get into thewhys of this later on. We'll playwith lists some more in a littlewhile.Before we get to our nextsample program, let's look at afew other things about Python.contents

PROGRAM IN PYTHON - PART 2be the space after 'time'.We briefly discussed stringsin Part 1. Let's look at string abit closer. A string is a series ofcharacters. Not much morethan that. In fact, you can lookat a string as an array ofcharacters. For example if weassign the string 'The time hascome' to a variable namedstrng, and then wanted toknow what the secondcharacter would be, we couldtype:strng 'The time has come'print strng[1]The result would be 'h'.Remember we always countfrom 0, so the first characterwould be [0], the second wouldbe [1], the third would be [2],and so on. If we want to findthe characters starting atposition 4 and going throughposition 8, we could say:print strng[4:8]which returns 'time'. Like ourfor loop in part 1, the countingstops at 8, but does not returnthe 8th character, which wouldWe can find out how longour string is by using the len()function:['The', 'time', 'has', 'come'].This is very powerful stuff.There are many other built-instring functions, which we'll beusing later on.The result from this code is:print len(strng)which returns 17. If we want tofind out where in our string theword 'time' is, we could usepos strng.find('time')Now, the variable pos (shortfor position) contains 4, sayingthat 'time' starts at position 4in our string. If we asked thefind function to find a word orsequence that doesn't exist inthe string like this:pos strng.find('apples')the returned value in pos wouldbe -1.We can also get eachseparate word in the string byusing the split command. Wewill split (or break) the string ateach space character by using:print strng.split(' ')which returns a list containingfull circle magazine #281,30,31]for cntr in range(0,12):print '%s has %ddays.' %(Months[cntr],DaysInMonth[cntr])There is one other thing thatI will introduce before we get toour next programmingexample. When we want toprint something that includesliteral text as well as variabletext, we can use what's calledVariable Substitution. To do thisis rather simple. If we want tosubstitute a string, we use '%s'and then tell Python what tosubstitute. For example, toprint a month from our listabove, we can use:print 'Month %s' %month[0]This would print 'Month Jan'. If we want to substitute aninteger, we use '%d'. Look atthe example below:Months Sep','Oct','Nov','Dec']DaysInMonth .days.days.days.days.days.days.days.Something important tounderstand here is the use ofsingle quotes and doublequotes. If you assign a variableto a string like this:st 'The time has come'or like this:st “The time has come”the result is the same.However, if you need to includea single quote in the string likethis:contents

PROGRAM IN PYTHON - PART 2st 'He said he's on hisway'code.you will get a syntax error. Youneed to assign it like this:st “He said he's on hisway”Think of it this way. To definea string, you must enclose it insome kind of quotes ‒ one atthe beginning, and one at theend ‒ and they must match. Ifyou need to mix quotes, usethe outer quotes to be the onesthat aren't in the string asabove. You might ask, what if Ineed to define a string like“She said “Don't Worry””? Inthis case, you could define itthis way:st 'She said “Don\'tWorry”'Notice the backslash beforethe single quote in 'Don't'. Thisis called an escape character,and tells Python to print the (inthis case) single-quote ‒without considering it as astring delimiter. Other escapecharacter sequences (to showjust a few) would be '\n' fornew line, and '\t' for tab. We'lldeal with these in later sampleWe need to learn a few morethings to be able to do our nextexample. First is the differencebetween assignment andequate. We've used theassignment many times in oursamples. When we want toassign a value to a variable, weuse the assignment operator orthe ' ' (equal sign):variable valueHowever, when we want toevaluate a variable to a value,we must use a comparisonoperator. Let's say we want tocheck to see if a variable isequal to a specific value. Wewould use the ' ' (two equalsigns):Don't worry about the if andthe colon shown in theexample above yet. Justremember we have to use thedouble-equal sign to doevaluation.if loop 12:The next thing we need todiscuss is comments.Comments are important formany things. Not only do theygive you or someone else anidea of what you are trying todo, but when you come back toyour code, say 6 months fromnow, you can be reminded ofwhat you were trying to do.When you start writing manyprograms, this will becomeimportant. Comments alsoallow you to make Pythonignore certain lines of code. Tocomment a line you use the '#'sign. For example:variable value# This is a commentSo, if we have a variablenamed loop and we want tosee if it is equal to, say, 12, wewould use:You can put commentsanywhere on a code line, butremember when you do,Python will ignore anythingafter the '#'.if loop 12:full circle magazine #28Now we will return to the "if"statement we showed brieflyabove. When we want to makea decision based on values ofthings, we can use the ifstatement:This will check the variable'loop', and, if the value is 12,then we do whatever is in theindented block below. Manytimes this will be sufficient,but, what if we want to say If avariable is something, then dothis, otherwise do that. Inpseudo code you could say:if x y thendo somethingelsedo something elseand in Python we would say:if x y:do somethingelse:do something elsemore things to doThe main things toremember here are:1. End the if or else statements9contents

PROGRAM IN PYTHON - PART 2with a colon.2. INDENT your code lines.Assuming you have morethan one thing to check, youcan use the if/elif/else format.For example:x 5if x 1:print 'Xelif x 6:print 'X6'elif x 10:print 'X10'else:print 'Xgreater'is 1'is less thanis less thanis 10 orNotice that we are using the' ' operator to see if x is LESSTHAN certain values - in thiscase 6 or 10. Other commoncomparison operators would begreater than ' ', less than orequal to ' ', greater than orequal to ' ', and not equal'! '.Finally, we'll look at a simpleexample of the whilestatement. The whilestatement allows you to createa loop doing a series ofloop 1steps over and over,while loop 1:until a specificresponse raw input("Enter something or 'quit' to end ")if response 'quit':threshold has beenprint 'quitting'reached. A simpleloop 0example would beelse:assigning a variableprint 'You typed %s' % response“loop” to 1. Then whilethe loop variable is less quitquittingthan or equal to 10, print theIn this example, we arevalue of loop, add one to it andcombining the if statement,Notice that when we typedcontinue, until, when loop iswhile loop, raw input'QUIT', the program did notgreater than 10, quit:statement, newline escapestop. That's because we aresequence, assignmentloop 1evaluating the value of theoperator, and comparisonwhile loop 10:response variable to 'quit'operator ‒ all in one 8 lineprint loop(response 'quit'). 'QUIT'loop loop 1program.does NOT equal 'quit'.run in a terminal wouldproduce the following output:Running this example wouldproduce:12345678910Enter somethingend FROGYou typed FROGEnter somethingend birdYou typed birdEnter somethingend 42You typed 42Enter somethingend QUITYou typed QUITEnter somethingendThis is exactly what wewanted to see. Fig.1 (aboveright) is a similar example thatis a bit more complicated, butstill simple.full circle magazine #2810or 'quit' toor 'quit' toor 'quit' toor 'quit' toor 'quit' toOne more quick examplebefore we leave for this month.Let's say you want to check tosee if a user is allowed toaccess your program. Whilethis example is not the bestway to do this task, it's a goodway to show some things thatwe've already learned.Basically, we will ask the userfor their name and a password,compare them with informationthat we coded inside theprogram, and then make adecision based on what wefind. We will use two lists ‒ oneto hold the allowed users andcontents

PROGRAM IN PYTHON - PART 2one to hold the passwords.Then we'll use raw input to getthe information from the user,and finally the if/elif/elsestatements to check anddecide if the user is allowed.Remember, this is not the bestway to do this. We'll examineother ways in later articles.Our code is shown in the boxto the right.Save this as'password test.py' and run itwith various inputs.The only thing that wehaven't discussed yet is in thelist checking routine startingwith 'if usrname in users:'.What we are doing is checkingto see if the user's name thatwas entered is in the list. If itis, we get the position of theuser's name in the list users.Then we useusers.index(usrname) to getthe position in the users list sowe can pull the password,stored at the same position inthe passwords list. Forexample, John is at position 1in the users list. His password,'dog' is at position 1 of thepasswords list. That way wecan match the two. Should password test.py#example of if/else, lists, assignments,raw input,#comments and --------# Assign the users and passwordsusers ['Fred','John','Steve','Ann','Mary']passwords -------------------------------------# Get username and passwordusrname raw input('Enter your username ')pwd raw input('Enter your password ')#----------------------------------------------# Check to see if user is in the listif usrname in users:position users.index(usrname) #Get the position in the list of the usersif pwd passwords[position]: #Find the password at positionprint 'Hi there, %s. Access granted.' % usrnameelse:print 'Password incorrect. Access denied.'else:print "Sorry.I don't recognize you. Access denied."pretty easy to understand atthis point.is owner of,aconsulting company in Aurora,Colorado, and has beenprogramming since 1972. Heenjoys cooking, hiking, music,and spending time with hisfamily.full circle magazine #2811contents

HOW-TOFCM#27-28 - Python Parts 1-2DevCD/DVDGraphics Internet M/media SystemHDDUSB Drive LaptopWirelessIn the last article, welearned about lists, literalsubstitution, comments,equate versus assignment,if statements and whilestatements. I promised you thatin this part we would learnabout modules and functions.So let's get started.ModulesModules are a way to extendyour Python programming. Youcan create your own, or useProgram In Python - Part 3those that come with Python,or use modules that othershave created. Python itselfcomes with hundreds ofvarious modules that makeyour programming easier. A listof the global modules thatcome with Python can be foundathttp://docs.python.org/modindex.html. Some modules areoperating system specific, butmost are totally cross platform(can be used the same way inLinux, Mac and MicrosoftWindows). To be able to use anexternal module, you mustimport it into your program.One of the modules that comeswith Python is called 'random'.This module allows you togenerate pseudo-randomnumbers. We'll use the moduleshown above right in our firstexample.Let's examine each line ofcode. The first four lines arecomments. We discussed themin the last article. Line five tellsPython to use the randommodule. We have to explicitlyfull circle magazine #29tell Python todo this.# # random example.py# Module example using the random module# import random# print 14 random integersfor cntr in range(1,15):print random.randint(1,10)Line sevensets up a 'for'loop to print 14randomnumbers. Lineeight uses therandint() function to print arandom integer between 1 and10. Notice we must tell Pythonwhat module the functioncomes from. We do this bysaying (in this case)random.randint. Why evencreate modules? Well, if everypossible function were includeddirectly into Python, not onlywould Python becomeabsolutely huge and slow, butbug fixing would be anightmare. By using modules,we can segment the code intogroups that are specific to acertain need. If, for example,you have no need to usedatabase functionality, youdon't need to know that thereis a module for SQLite.However, when you need it, it'salready there. (In fact, we'll be7using database modules lateron in this series.)Once you really get startedin Python programming, youwill probably make your ownmodules so you can use thecode you've already writtenover and over again, withouthaving to re-type it. If you needto change something in thatgroup of code, you can, withvery little risk of breaking thecode in your main program.There are limits to this and wewill delve into this later on.Now, when we used the 'importrandom' statement earlier, wewere telling Python to give usaccess to every function withinthe random module. If,however, we only needed touse the randint() function, wecontents

PROGRAM IN PYTHON - PART 3can re-work the importstatement like this:from random import randintNow when we call ourfunction, we don't have to usethe 'random.' identifier. So, ourcode changes tofrom random import randint# print 14 random integersfor cntr in range(1,15):print randint(1,10)FunctionsWhen we imported therandom module, we used therandint() function. A function isa block of code that isdesigned to be called, usuallymore than once, which makesit easier to maintain, and tokeep us from typing the samecode over and over and over.As a very general and grossstatement, any time you haveto write the same code morethan once or twice, that code isa good candidate for afunction. While the followingtwo examples are silly, theymake good statements aboutusing functions. Let's say wewanted to take two numbers,add them, thenmultiply them, andthen subtract them,displaying thenumbers and resultseach time. To makematters worse, wehave to do that threetimes with three setsof numbers. Our sillyexample would thenlook like the textshown right.#silly exampleprint 'Adding the two numbers %d and %d print 'Multiplying the two numbers %d andprint 'Subtracting the two numbers %d andprint '\n'print 'Adding the two numbers %d and %d print 'Multiplying the two numbers %d andprint 'Subtracting the two numbers %d andprint '\n'print 'Adding the two numbers %d and %d print 'Multiplying the two numbers %d andprint 'Subtracting the two numbers %d andprint '\n'%d ' % (1,2,1 2)%d %d ' % (1,2,1*2)%d %d ' % (1,2,1-2)%d ' % (1,4,

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