# define function to pause in tutorial
def pause():
  raw_input('...')
print '\n'*24
# class definition
print "# basic class definition"
print '>>> class X:\n e = 12 # class variable\n def m(x):  # method m\n   print "--> argument to method m is", x'
class X:
 e = 12 
 def m(x):
  print "--> argument to method m is", x
pause()
print "# print class variable and method (just to see what they are)"
print "print X.e, X.m"
print X.e, X.m
pause()
print "# create an instance of class X"
print "a = X()"
a = X()
pause()
print "# look at the instance variables"
print "print a.e, a.m"
print a.e, a.m
pause()
print "# write over the instance variable e"
print "a.e += 1"
a.e += 1
print "print a.e, X.e"
print a.e, X.e
pause()
print "# perhaps unexpected ... a.e is really an instance variable!"
print "# we can even add new instance variables on-the-fly"
print "# (these are called object attributes)"
print "a.q = [0,True]"
print "print a.q"
a.q=[0,True]
print a.q
pause()
print "try invoking the method of a"
print "a.m(100)"
print '''Traceback (most recent call last):
  File "C:\Documents and Settings\Ted Herman\Desktop\tutClass.py", line 41, in -toplevel-
    a.m(100)
TypeError: m() takes exactly 1 argument (2 given)'''
print "# does Python have a bug?!  how can m(100) have two given arguments?" 
pause()
print "# try the method of a with no arguments"
print "a.m()"
a.m()
pause()
print '# solution to riddle:  every method of a class is passed a "secret", first'
print '# argument:  it is the "self" parameter, the object handle'
print '# so we rewrite X to expect this'
print '>>> class X:\n e = 12 # class variable\n def m(self,x):  # method m\n   print "--> argument to method m is", x'
class X:
 e = 12 
 def m(self,x):
  print "--> argument to method m is", x
print "a = X()  # let a become an instance of class X"
a = X()
print "# now try a.m(100)"
print "am.(100)"
a.m(100)
print "# that's better!"
pause()
print "# let's look at an example where a method uses instance variables"
pause()
print '''class Y:
 rememb = []
 def deq(self):
   if len(self.rememb)>0:
      r = self.rememb[0]
      self.rememb = self.rememb[1:]
      return r
   else: return None
 def enq(self,item):
   self.rememb.append(item)'''
class Y:
 rememb = []
 def deq(self):
   if len(self.rememb)>0:
      r = self.rememb[0]
      self.rememb = self.rememb[1:]
      return r
   else: return None
 def enq(self,item):
   self.rememb.append(item)
print "# create an instance of Y"
print "b = Y()"
print "print b.deq()"
b = Y()
print b.deq()
pause()
print "# demonstrate methods of object b"
print "b.enq(99)"
print "b.enq(100)"
b.enq(99)
b.enq(100)
print "# let's spy on b, looking at its rememb attribute"
print "print b.rememb"
print b.rememb
print "# print some deq() applications of b"
print "for i in range(0,3):  print b.deq()"
for i in range(0,3): print b.deq()
pause()
print "# what if we want to construct an object with some initialization parameters?"
print "# solution:  define a constructor method (called __init__)"
print '''class Z:
 def __init__(self,x,y):
    self.coord = [x,y]
 def xpos(self):
    return self.coord[0]'''
class Z:
 def __init__(self,x,y):
    self.coord = [x,y]
 def xpos(self):
    return self.coord[0]
print "v = Z(40,200)"
v = Z(40,200)
print "print v.xpos()"
print v.xpos()
pause()
print "# create some instances of Z"
print "z1 = Z(2,6)"
print "z2 = Z(2,6)"
print "z3 = z2"
z1 = Z(2,6)
z2 = Z(2,6)
z3 = z2
print "# now test if they are the same ..."
print "z2 == z3"
print z2 == z3
print "z1 == z2"
print z1 == z2
print "# is this a bug?"
pause()
print "# answer:  z2 and z3 refer to the same object, so they are equal;"
print "# whether z1 and z2 are equal depends on your point of view,"
print "# but Python does allow us to extend operators ==, >, <, etc for"
print "# whatever kind of object we like, for instance ..."
print '''class Q:
 def __init__(self,x,y):
    self.coord = [x,y]
 def __eq__(self,other):
    return self.coord == other.coord
 def xpos(self):
    return coord[0]'''
class Q:
 def __init__(self,x,y):
    self.coord = [x,y]
 def __eq__(self,other):
    return self.coord == other.coord
 def xpos(self):
    return self.coord[0]
print "# now create instances and compare"
print "w1 = Q(2,6)"
print "w2 = Q(2,6)"
print "w3 = Q(2,7)"
w1 = Q(2,6)
w2 = Q(2,6)
w3 = Q(2,7)
print "w1 == w2"
print w1 == w2
print "w2 == w3"
print w2 == w3
pause()

print "# not covered: how to use inheritance, multiple inheritance in defining classes"
print "# also not covered:  how to define new types of exception (using classes)"