Programming for Engineers in Python

Recitation 4

Programming for Engineers in Python1AgendaSample problemsHash functions & dictionaries (or next week)Car simulation22A function can be an argument3def do_twice(f):f()f()def print_spam():print 'spam'>>> do_twice(print_spam)spamspamFermats last theorem4Pierre de Fermat1601-1665

Fermats last theorem5>>> check_fermat(3,4,5,2)No, that doesn't work>>> check_fermat(3,4,5,3)No, that doesn't workDirty shortcut since 1995:def check_fermat(a,b,c,n):print "Wiles proved it doesnt work"

Sir Andrew John Wiles1953-Cumulative sum6For a given list A we will return a list B such that B[n] = A[0]+A[1]+A[n]Take 1:def cumulative_sum(lst):summ = [ lst[0] ] * len(lst)for i in range(1, len(lst)): summ[i] = summ[i-1] + lst[i]return summ Take 2:def cumulative_sum(lst):return [sum(lst[0:n]) for n in range(1, len(lst)+1)]Estimating e by its Taylor expansion7from math import factorial, e

term = 1summ = 0k = 0while term > 1e-15: term = 1.0/factorial(k) summ += term k += 1

print "Python e:", eprint Taylors e:", summprint Iterations:, k

Brook Taylor, 1685-1731Estimating by the Basel problem8from math import factorial, pi, sqrt

term = 1summ = 0k = 1while term > 1e-15: term = 1.0/k**2 summ += term k += 1summ = sqrt(summ*6.0)

print "Python pi:", piprint Eulers pi:", summprint Iterations:, k

Leonard Euler,1707-1783Ramanujans estimation (optional)9from math import factorial, pi

term = 1summ = 0k = 0while term > 1e-15: term = factorial(4.0*k) / factorial(k)**4.0 term *= (1103.0+26390.0*k) / 396.0**(4.0*k) summ += term k += 1summ = 1.0/(summ * 2.0*2.0**0.5 / 9801.0)

print "Python Pi:", piprint "Ramanujan Pi:", summprint Iterations:, k

Srinivasa Ramanujan, 1887-1920Triple Double Word10We want to find a word that has three double letters in it, like aabbcc (which is not a word!)Almost qualifiers:CommitteeMississippiWrite a function to check if a word qualifiesWrite a function that reads a text file and checks all the words Code: http://www.greenteapress.com/thinkpython/code/cartalk.pyCorpus: http://www.csie.ntu.edu.tw/~pangfeng/Fortran%20examples/words.txtPyGame11A set of Python modules designed for writing computer gamesDownload & install:http://pygame.org/ftp/pygame-1.9.2a0.win32-py2.7.msi

Car game12Control a car moving on the screenYouTube demo: http://www.youtube.com/watch?v=DMOj3HpjemECode: https://gist.github.com/1372753 or in car.pyCar controlled by arrowsHonk with EnterExit with ESC

ToDo List:13Fix stirring problemHonk by pressing spaceCar will go from the bottom to top and from one side to the other (instead of getting stuck)Switch to turtle!2 players car game14Collision avoidance simulator:When the cars are too close one of them honksPlayers need to maneuver the cars to avoid honksCode: https://gist.github.com/1380291 or cars.pyRed car controlled by arrowsBlue car controlled by z, x, c, s