CSC102 INTRO TO PROGRAMMING WITH PYTHON LECTURE 22 CLASS MICHAEL GROSSBERG

Transcription

1 CSC102 INTRO TO PROGRAMMING WITH PYTHON LECTURE 22 CLASS MICHAEL GROSSBERG

2 TYPES INT BOOLEAN FLOAT COMPLEX STRINGS SETS DICTIONARIES LISTS I WANT MY OWN TYPES!

3 CLASSES = DIY TYPES BASIS OF OBJECT ORIENTED PROGRAMMING

4 BIG IDEA: TREE STRUCTURE PROCEDURAL PROGRAMMING

5 COLLECTIVE STRUCTURE OBJECTED ORIENTED PROGRAMMING

6 CLASSES TYPE: OBJECTS INSTANCES WORKER BEE MANY QUEEN BEE ONE HIVE ONE CLASS INSTANCE

7 PILLARS OF OOP ABSTRACTION DATA + ACTION BUNDLED ENCAPSULATION INFORMATION HIDING (SPYS: DON T NEED TO KNOW WHY) INHERITANCE CODE REUSE COPY CLASS WITH ADDITIONS POLYMORPHISM SAME FUNCTION DOES RIGHT THING FOR RIGHT TYPE

8 2D POINT p x = 1.55 y = 3.99 WISH LIST: EASY TO MAKE EASY TO GET X AND Y STR(P) = (1.55,3.99) ADD POINTS TOGETHER MULT POINT BY SCALER

9 EXAMPLE CLASS: POINT # This defines a new class class Point(object): pass class: SPECIAL KEYWORD LIKE def BUT FOR DEFINING CLASSES NOT ABSOLUTELY NEEDED object IS MOTHER OF ALL (NEW) CLASSES DOESN T DO ANYTHING YET

10 CAN MAKE ATTRIBUTES ON FLY class Point(object): pass origin = Point() origin.x = 0 origin.y = 0 OK TO DO IN PROTOTYPING

11 PRINT DOESN T SHOW X,Y origin = Point() origin.x = 0 origin.y = 0 print 'origin = ',origin THIS PRINTS x y ARE ATTRIBUTES OF ORIGIN (A POINT) origin = < main.point object at 0x13ea5910> NEED TO PRINT X,Y MANUALLY

12 EXAMPLE PROGRAM import sys class Point(object): pass def main(): origin = Point() origin.x = 0 origin.y = 0 p = Point() print 'origin = ',origin print 'origin = (%f,%f)' % (origin.x,origin.y) print 'p = ',p try: print 'p = (%f,%f)' % (p.x,p.y) except Exception, e: sys.stderr.write(str(e)+'\n') KABOOM! JUST DEFINING A NEW POINT DOESN T MEAN IT HAS AN X AND Y if name == ' main ': main() NEED TO SET ATTRIBUTES EACH TIME

13 CONSTRUCTOR class Point(object): def init (self, x=0, y=0): self.x = x self.y = y def: DEFINE A FUNCTION TO DEFINE WHAT HAPPENS WHEN YOU CALL Point() init : SPECIAL NAME (LIKE KEYWORD) ONLY USED FOR SETTING UP CLASS CONSTRUCTOR: INITIALIZES THINGS

14 SELFISH class Point(object): def init (self, x=0, y=0): self.x = x self.y = y self: KEYWORD DON T KNOW WHAT POINT WILL BE CALLED: WE CALL IT THIS OBJECT self self: ALWAYS, ALWAYS FIRST ARGUMENT OF EVERY FUNCTION IN CLASS* *ADVANCED EXCEPTIONS TO THIS RULE BUT NEVERMIND

15 DEFINE INIT class Point(object): 'A class to the data for a mathematical point' def init (self, x=0, y=0): self.x = x self.y = y LIKE A COMMENT def main(): origin = Point() print 'origin = (%f,%f)' % (origin.x,origin.y) p = Point(x=1,y=1) print 'p = (%f,%f)' % (p.x,p.y) if name == ' main ': main() SET OR GET DEFAULTS

16 PRINT THYSELF class Point: 'A class to the data for a mathematical point' def init (self, x=0, y=0): self.x = x self.y = y def str (self): return '(%f,%f)' % (self.x,self.y) def main(): origin = Point() print 'origin = ',origin p = Point(x=1,y=1) print 'p = ',p print 'str(p) = '+str(p) if name == ' main ': main() NOW STR WORKS!

17 LENGTH OF A POINT (VECT) sqrt(x**2+y**2) P y ORIGIN x norm(p)? p.norm()

18 CUSTOM METHODS class Point: 'A class to the data for a mathematical point' def init (self, x=0, y=0): self.x = x self.y = y def norm(self): return math.sqrt(self.x**2 + self.y**2) def str (self): return '(%f,%f)' % (self.x,self.y) def main(): origin = Point() print 'origin = ',origin print 'origin.norm() = ',origin.norm() p = Point(x=1,y=1) print 'p = ',p print 'p.norm() = ',p.norm() BUNDLE USEFUL METHODS WITH CLASS

19 DON T ACT SHOCKED my_string.reverse() my_list.pop() my_set.pop() my_dictionary.keys() WE HAVE SEEN THIS MANY TIMES BEFORE

20 MAKE YOUR OWN + foo + bar == foobar HOW DO WE REDEFINE OPERATORS?

21 ADDING POINTS P Q ORIGIN M=P+Q Q m.x = p.x+q.x m = p+q <=> m.y = p.y+q.y

22 OPERATOR OVERLOADING import math class Point: 'A class to the data for a mathematical point' def init (self, x=0, y=0): self.x = x self.y = y def norm(self): return math.sqrt(self.x**2 + self.y**2) def add (self,other): return Point(x=self.x+other.x,y=self.y+other.y) def str (self): return '(%f,%f)' % (self.x,self.y) def main(): origin = Point() print 'origin = ',origin p=point(x=1,y=1) print 'p = ',p print 'origin + p = ', origin+p print 'origin + p + p = ', origin+p+p if name == ' main ': main()

23 OVERLOADING MULTIPLICATION class Point: 'A class to the data for a mathematical point' def init (self, x=0, y=0): self.x = x self.y = y def norm(self): return math.sqrt(self.x**2 + self.y**2) def add (self,other): return Point(x=self.x+other.x,y=self.y+other.y) def sub (self,other): return Point(x=self.x-other.x,y=self.y-other.y) def neg (self): return Point(x=-self.x,y=-self.y) def mul (self,other): return Point(x=self.x*other,y=self.y*other) def str (self): return '(%f,%f)' % (self.x,self.y) def main(): origin = Point() print 'origin = ',origin p=point(x=1,y=1) print 'p = ',p print '-p = ',-p print 'origin - p = ', origin-p print 'origin + p*2 = ', print origin+ p*2 try: print 'origin + 2*p = ', print origin+ 2*p except Exception, e: print sys.stderr.write( str(e)+'\n') LIKE ADD WITH MULT SELF MUST BE ON LEFT

24 RMUL (SELF RIGHT) class Point: 'A class to the data for a mathematical point' def init (self, x=0, y=0): self.x = x self.y = y def norm(self): return math.sqrt(self.x**2 + self.y**2) def add (self,other): return Point(x=self.x+other.x,y=self.y+other.y) def sub (self,other): return Point(x=self.x-other.x,y=self.y-other.y) def neg (self): return Point(x=-self.x,y=-self.y) def mul (self,other): return Point(x=self.x*other,y=self.y*other) def rmul (self,other): return Point(x=self.x*other,y=self.y*other) def str (self): return '(%f,%f)' % (self.x,self.y)

25 BOTH SIDES NOW (MULT) def main(): origin = Point() print 'origin = ',origin p=point(x=1,y=1) print 'p = ',p print 'origin + p*2 = ', origin+ p*2 print 'origin + 2*p = ', origin+ 2*p if name == ' main ': main() MULT FIXED

26 FIRE WHEN READY def main(): muzzle_velocity = 240 # meters/sec angle = 45. # degrees angle_rad = (angle/360.)*2*math.pi gravity = 9.78*Point(x=0,y=-1) time_step = 1./10. # seconds v = muzzle_velocity*point( x=math.cos(angle_rad), y=math.sin(angle_rad)) pos = Point(x=0,y=0) pos_x,pos_y = [],[] pos_x.append(pos.x) pos_y.append(pos.y) for time in range(1,400): v = v+time_step*gravity pos = pos + v pos_x.append(pos.x) pos_y.append(pos.y) fig = pylab.figure() ax = fig.add_subplot(1,1,1) ax.plot(pos_x,pos_y) ax.plot([pos_x[0],pos_x[-1]], [0,0], 'k-') pylab.show() POINT KEEPS TRACK OF POSITION OR VELOCITY

27 TERMINATE ON IMPACT def main(): muzzle_velocity = 240 # meters/sec angle = 45. # degrees angle_rad = (angle/360.)*2*math.pi gravity = 9.78*Point(x=0,y=-1) time_step = 1./10. # seconds v = muzzle_velocity*point( x=math.cos(angle_rad), y=math.sin(angle_rad)) pos = Point(x=0,y=0) pos_x,pos_y = [],[] pos_x.append(pos.x) pos_y.append(pos.y) for time in range(1,400): v = v+time_step*gravity pos = pos + v if pos.y <0: break pos_x.append(pos.x) pos_y.append(pos.y) STOP WHEN YOU HIT THE GROUND

28 MOVIE MAKING def make_animation(pos_x,pos_y): min_x, max_x = min(pos_x), max(pos_x) min_y, max_y = min(pos_y), max(pos_y) for ind,(x,y) in enumerate(zip(pos_x,pos_y)): fig = pylab.figure() ax = fig.add_subplot(1,1,1) ax.plot(pos_x[:ind],pos_y[:ind],'b-') ax.plot(pos_x[ind],pos_y[ind],'k.',markersize=10.) ax.plot([pos_x[0],pos_x[-1]],[0,0],'k-') ax.set_xlim([min_x,max_x]) ax.set_ylim([min_y,max_y]) fig.savefig('./projectile_images/projectile_%03d.png' % ind) command = ('mencoder', 'mf://projectile_images/*.png', '-mf', 'type=png:w=800:h=600:fps=25', '-ovc', 'lavc', '-lavcopts', 'vcodec=mpeg4', '-oac', 'copy', '-o', 'projectile.avi') print "\n\nabout to execute:\n%s\n\n" % ' '.join(command) subprocess.check_call(command) JUST FOR FUN REQUIRERS MENCODER

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30 THANKS