class A(object):  def show(self):  print 'base show'   class B(A):  def show(self):  print 'derived show'  obj = B()  obj.show()

obj.__class__ = Aobj.show()

class A(object): def __init__(self,a,b): self.__a = a self.__b = b def myprint(self): print 'a=', self.__a, 'b=', self.__b a1=A(10,20) a1.myprint() a1(80)

class A(object): def __init__(self, a, b): self.__a = a self.__b = b def myprint(self): print 'a=', self.__a, 'b=', self.__b def __call__(self, num): print 'call:', num + self.__a

class B(object):  def fn(self):  print 'B fn'  def __init__(self):  print "B INIT"  class A(object):  def fn(self):  print 'A fn'  def __new__(cls,a):  print "NEW", a  if a>10:  return super(A, cls).__new__(cls)  return B()  def __init__(self,a):  print "INIT", a  a1 = A(5)  a1.fn()  a2=A(20)  a2.fn()

NEW 5 B INIT B fn NEW 20 INIT 20 A fn

ls = [1,2,3,4]  list1 = [i for i in ls if i>2]  print list1  list2 = [i*2 for i in ls if i>2]  print list2  dic1 = {x: x**2 for x in (2, 4, 6)}  print dic1  dic2 = {x: 'item' + str(x**2) for x in (2, 4, 6)}  print dic2  set1 = {x for x in 'hello world' if x not in 'low level'}  print set1

[3, 4]   [6, 8] {2: 4, 4: 16, 6: 36} {2: 'item4', 4: 'item16', 6: 'item36'} set(['h', 'r', 'd'])

num = 9   def f1():  num = 20  def f2():  print num  f2()  f1()  f2()

9  9

num = 9  def f1():      global num      num = 20  def f2():     print num  f2()  f1()  f2()  # prints:  #      9  #      20

a=8  b=9

(a,b) = (b,a)

class A(object):  def __init__(self,a,b):  self.a1 = a  self.b1 = b  print 'init'  def mydefault(self):  print 'default'  a1 = A(10,20)  a1.fn1()  a1.fn2()  a1.fn3()

defaultdefaultdefault

class A(object): def __init__(self,a,b):  self.a1 = a  self.b1 = b  print 'init'  def mydefault(self):  print 'default'  def __getattr__(self,name):  return self.mydefault  a1 = A(10,20)  a1.fn1()  a1.fn2()  a1.fn3()

class A(object):  def __init__(self,a,b):  self.a1 = a  self.b1 = b  print 'init'  def mydefault(self,*args):  print 'default:' + str(args[0])  def __getattr__(self,name):  print "other fn:",name  return self.mydefault a1 = A(10,20)  a1.fn1(33)  a1.fn2('hello')  a1.fn3(10)

__all__ = ['mod1','mod3']

def mulby(num):  def gn(val):  return num * val  return gn  zw = mulby(7)  print(zw(9));

def strtest1(num):  str='first'  for i in range(num):  str+="X"  return str