python programming.doc

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Electrical Engineering & Computer Science
Y U Liu

Chap 1 • computer o machine for executing a program o hardware • program o detailed step-by-step instructions o software  coding - the art of programing/making software • programing languages o high-level - what humans talk in  translated via compilers and interpreters  compiler  takes source code (program) and translates it to machine code (program that a comp can directly execute)  faster then interpreters, only need code once  interpreter  source codes directly to output  more flexible and portable  python o low-level - what computers talk in  machine language - #'s  assembly language - abbreviations (translated via assemblers)  not portable, hardware dependent o syntax - precise programming language form o semantics - precise programming language meaning • finding what can be computed o algorithm  recipe for victory o analysis  a mathmatical look at algorithms  will the algorithm be intractable (not practical) o experimentation  trail and error • • CPU - central processing unit o brain, where basic operations are carried out o fetch, decode, execute • memory o RAM - random access memory  main memory, gets lost when comp gets shut down o secondary memory  hard drive, CD, ect. • definitions o prompt - >>> o statement - complete command o command shell - interactive environment to interact w/an interpreter o parameters - arguments (stuff,in,here) 3 o module or script - where programs can be written and stored o programming environment - simplifies the process of programing (IDLE) o comments - # not read by python o variable - used when giving a name to a value (x=3) • interpreters o stimulates a computer that understands high-level language o analyzes and executes source code instruction by instruction o source code and interpreter are needed each time the program is run o more flexible then compiler since they can run interactively o more portable (runs on mac, pc) o python is an interpreter • Bit - one binary digit (0 or 1) • Byte - 8 bits • 1KB = 10^3 Bytes • 1Mb = 10^6 Bytes • 1GB = 10^9 Bytes • python stuff • input -> computation -> output • lines that start w/# r called comments • variables o data holders o can be reassigned as much as you want o the names you give them are called identifiers  must begin w/a letter or underscore  case sensitive o NameError happens when a variable w/out a value assigned is used o reserved words - identifiers python permanently has • expressions o fragments of code that produce or calc new data o literals: 2, 5+4 o simple identifiers can be expression • input o gets input from user and stores it as a variable • definite loops o variable for - loop index o range starts w/0 to whatever in sequence o list turns the thing into a list Chap 2/3 • IPO - input, process, output • identifiers o includes varibles o must begin with a letter or _ o case-sensitive o reserved/keywords - already identifiers (python claims them) • expression - produces or calculates new data o literal - used to indicate specific value (32) o strings - textual data ("hi","32") o identifiers can be expressions • operators o + - * / ** % (remainder), // (integer division)  7//3 = 2  3//7 = 0  17//9 = 1  12%11 = 1  11%12 = 11  101//100 = 1  -101/100 = -2 • keyword end o overrides adding an extra line o print('sup', end=' mh') print('yes')  sup mhyes • assignment statement o = • input statement o for a string: = input() o for a value: = eval(input()) • loop - executes a sequence of statements multiple times in succession o loop index - var after for o for odd in [1,3,5]: print(odd*odd)  1 9 25 • range() o a = list(range(3)) print(a)  [0, 1, 2] o a = list(range(0,12,3)) print(a)  [0, 3, 6, 9] • data - info stored and manipulated by comp programs o you can get a data type by typing type() o type(3)  o type(3.0)  • library - module that contains useful definitions o from library import * • bits o each bit has 2 possible values: 0, 1 (on, off) o typical comps have 32 or 64 bits o for a 32 bit int representation,smallest # it can store is -2^31 and largest is 2^31- 1 o numbers that exceed this get turned in scientific notation (kills accuracy a bit) • explicit type conversion o int(4.5)  4 o float(4)  4.0 o round(math.pi, 2)  3.14 memory organization • Bit - one binary digit (0 or 1) • Byte - 8 bits • 1KB = 10^3 Bytes • 1Mb = 10^6 Bytes • 1GB = 10^9 Bytes types of errors • syntax o something is wrong w/ur grammar o caught by interperater o easy to fix • run-time error o ex. divide by 0, program gets stuck o not caught by interperater o not so easy to fix • logic error • o error in design, even if the coding works • stored information - data o int - reserved word for integer o float - reserved word for floating point (fractional parts ex. 2.34) o integer divsion  10//3 = 3 o remainder division  10%3 = 1 Chap 4 graphics • Tkinter - pythons GUI (graphical user interface) module • object - a computational entity that combines data and operations o they kno and can do stuff o its data is stored in instance variables, and its operations are called methods from graphics import * def main(): win = GraphWin("Draw A House", 400,500) #name of window, pixels win.setCoords(0,0,20,20) #coordinates bottom left to top right win.setBackground('red') #sets background red p1base = win.getMouse() p2base = win.getMouse() #gets a mouseclick base = Rectangle(p1base,p2base) base.draw(win) #draws the object in window p3roof = win.getMouse() p3base = Point(p2base.getX(),p1base.getY()) #gets X and Y coordinates of mouseclicks roof = Polygon(p1base, p3roof, p3base) roof.draw(win) center = win.getMouse() window = Circle(Point(center.getX(),center.getY()), 1) window.setFill('blue') #sets fill color to blue window.setOutline('green') #sets outline color to green window.draw(win) text = Text(Point(center.getX(),center.getY()), 'this is text') #centers text on the window text.draw(win) inpt = Entry(Point(2,2),3) #entry point, a spot for a user to put things inpt.setText("0") #sets entry text inpt.draw(win) win.getMouse() ha = eval(inpt.getText()) #lets the program read the txt in the entry box window.move(ha,ha) #moves the circle that many units window2 = window.clone() #clones object window2.move(-2,2) window2.draw(win) win.getMouse() win.close() #closes the program main() • pg 108 starts a list of methods Chap 5 string, lists, and files (dis ex #1-4 prg ex #15, 16) • string operations o def main(): a = 'abcd efg' print(a[3],a[-1],a[4:]) #string indexing. the last is called splicing specifically print(len(a)) #gets length of string for ch in a: print(ch, end=' ') #iteration through characters main()  d g efg 8 a b c d e f g • lists (can be composed of not only numbers, but strings as well) o def main(): myn = [1,2,3,4] print(myn[2]) #gets the n+1 thing in the list myn[2] = 0 #changes the list thing print(myn) main()  3 [1, 2, 0, 4] o lists are mutable, their values can be changed:  x = [1,2,3] x[1:3] = "yes", "no" print(x)  [1, 'yes', 'no'] • Types of codes o ASCII (American Standard Code for Information Interchange)  uses the #'s 0-127 o Unicode  much larger standard, what python uses o getting code in python  ord('a') = 97 #gets the unicode number  chr(97) = 'a' #gets the symbol for the unicode number • encoder program o CB = open('codebook.txt','r') CB = CB.readline() #Read the codebook from the file MT = open("message.txt", "r") MT = MT.readline() #Read the plaintext from the file msg = "" #starts message off with nothing for i in MT.split(): #splits the string into substrings for each space for ch in i: new = CB[(ord(ch)-97)%26] msg = msg+new msg = msg+' ' msg=msg.rstrip() pos=(-3)%len(msg) #Rotates the -3 positions msg = msg[pos:]+msg[:pos] #adds the beginning (-3) outfile = open("encoded_message.txt", "w") #Writes the encoded message into a file called “encoded_message.txt” print(msg, file=outfile) # " " outfile.close() o def main(): instring = '83 110 33' message = '' for ch in instring.split(): #splits the numbers codename = eval(ch) #gets the number message = message+chr(codename) #adds the letter print(message) main()  sn! • list method o squares = [] for x in range(1,10): squares.append(x*x) #adds to the empty list each loop print(squares)  [1, 4, 9, 16, 25, 36, 49, 64, 81] • turning: o strings into values  int(" ")  eval can not have a leading 0, but int can  int('05')  5  eval('05')  error o values into strings  str(500)  '500' • usefullness of turning o day, month1, year = eval(input('enter day, month, and year numbers: ')) #gets 3 inputs at once and stores them date1 = str(month1) + "/" + str(day) + "/" #adds the recently converted strings together month2 = ['jan','feb','mar','apr','may','june','july','aug','sept','oct','nov','dec'] #list of months monthStr = month2[month1-1] date2 = monthStr+' '+str(day)+', '+str(year) print(date1, 'or', date2 + '.') • formating strings o .format()  print('grwar {0:10.2} done'.format(8.345))  grwar 8.3 done  print('grwar {0:0.5f} done'.format(8.345))  grwar 8.34500 done Chap 6 functions • advantages of functions o do not have to write multiple codes o easier to maintain if a change is desired inside the code • part of a program that creates a function - function definition • define functions before main o def happy(): print("Happy Birthday to You.") #defines the function happy def sing(person): happy() #uses the function happy happy() print("Happy Birthday dear", person+".") #adds an extra line, in which the has a changeable variable happy() def main(): sing('Marry') #sings w/changeable variable in the main function  Happy Birthday to You. Happy Birthday to You. Happy Birthday dear Marry. Happy Birthday to You. o def sumdiff(x,y): #gets 2 parameters sum = x+y diff = x-y return sum, diff #returns 2 values def main(): num1,num2 = eval(input("get it")) s,d = sumdiff(num1,num2) print(s, d) main()  get it 55,4 59 51 o def addinterest(balances, rate): for i in range(len(balances)): #figure out this for loop balances[i] = balances[i]*(1+rate) #balance[1] = balance[1]*(rate+1). balance[2] = forth return balances[i] #returns balances 0 - len-1 def main(): amounts = [1000,2200,800,360] rate = .05 addinterest(amounts,rate) print(amounts) main()  [1050.0, 2310.0, 840.0, 378.0] o Chap 7 simple decisions • decision structures- statements that allow a program to execute different sequences of instruction in different cases • != is not equal to • if, elif, else o a,b,c = eval(input("enter 3 coefficents (a,b,c)")) #quadratic formula finder discrim = b*b - 4*a*c if discrim < 0: #if statement. if true this happens (these are called boolean expressions) print("no real roots") elif discrim == 0: #second if statement. if true this happens root = -b/(2*a) print("\ndouble root at", root) else: #if both are false, this happens discroot = math.sqrt(b*b-4*a*c) root1 = (-b+discroot)/(2*a) root2 = (-b-discroot)/(2*a) print("\nsolutions:", root1, root2) • exception handling • o try: except : o try: #the proggram trys to run a,b,c = eval(input("enter 3 coefficents (a,b,c)")) discrim = b*b - 4*a*c discroot = math.sqrt(b*b-4*a*c) root1 = (-b+discroot)/(2*a) root2 = (-b-discroot)/(2*a) print("\nsolutions:", root1, root2) except ValueError as exc0bj: #if something goes wrong it goes through these exceptions if str(excObj)=="math domain error": #one type of value error print("no Real Roots") else: #any other type of value error print("not enough coefficients") except SyntaxError: #this kind of error prints this statement print("not correct form, missing comma?") except: #another error prints this statement print("there is something wrong") • finding the max of so many values o n = eval(input("how many numbers?: ")) #user inputs how many numbers there are max = eval(input("enter a #: ")) #sets the first number user gives us to max for i in range(n-1): #loops through n times x = eval(input("next number: ")) #gets the value of the next number if x>max: #if this is true then: max = x #a new max is set print("largest number is", max) #prints the biggest number  how many numbers?: 4 enter a #: 2 next number: 4 next number: 3 next number: 5 largest number is 5 o or we could just use pythons build in max(x1, x2, x3) function... Chap 8 loop structures and booleans • while - the indefinite or conditional loop (both these functions print the numbers 0-10) o for i in range(11): #our old definite loop print(i) o i = 0 #new
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