AppPkg/Applications/Python/Python-2.7.2/Demo/classes/Range.py

   1 """Example of a generator: re-implement the built-in range function
   2 without actually constructing the list of values.
   3
   4 OldStyleRange is coded in the way required to work in a 'for' loop before
   5 iterators were introduced into the language; using __getitem__ and __len__ .
   6
   7 """
   8 def handleargs(arglist):
   9     """Take list of arguments and extract/create proper start, stop, and step
  10     values and return in a tuple"""
  11     try:
  12         if len(arglist) == 1:
  13             return 0, int(arglist[0]), 1
  14         elif len(arglist) == 2:
  15             return int(arglist[0]), int(arglist[1]), 1
  16         elif len(arglist) == 3:
  17             if arglist[2] == 0:
  18                 raise ValueError("step argument must not be zero")
  19             return tuple(int(x) for x in arglist)
  20         else:
  21             raise TypeError("range() accepts 1-3 arguments, given", len(arglist))
  22     except TypeError:
  23         raise TypeError("range() arguments must be numbers or strings "
  24         "representing numbers")
  25
  26 def genrange(*a):
  27     """Function to implement 'range' as a generator"""
  28     start, stop, step = handleargs(a)
  29     value = start
  30     while value < stop:
  31         yield value
  32         value += step
  33
  34 class oldrange:
  35     """Class implementing a range object.
  36     To the user the instances feel like immutable sequences
  37     (and you can't concatenate or slice them)
  38
  39     Done using the old way (pre-iterators; __len__ and __getitem__) to have an
  40     object be used by a 'for' loop.
  41
  42     """
  43
  44     def __init__(self, *a):
  45         """ Initialize start, stop, and step values along with calculating the
  46         nubmer of values (what __len__ will return) in the range"""
  47         self.start, self.stop, self.step = handleargs(a)
  48         self.len = max(0, (self.stop - self.start) // self.step)
  49
  50     def __repr__(self):
  51         """implement repr(x) which is also used by print"""
  52         return 'range(%r, %r, %r)' % (self.start, self.stop, self.step)
  53
  54     def __len__(self):
  55         """implement len(x)"""
  56         return self.len
  57
  58     def __getitem__(self, i):
  59         """implement x[i]"""
  60         if 0 <= i <= self.len:
  61             return self.start + self.step * i
  62         else:
  63             raise IndexError, 'range[i] index out of range'
  64
  65
  66 def test():
  67     import time, __builtin__
  68     #Just a quick sanity check
  69     correct_result = __builtin__.range(5, 100, 3)
  70     oldrange_result = list(oldrange(5, 100, 3))
  71     genrange_result = list(genrange(5, 100, 3))
  72     if genrange_result != correct_result or oldrange_result != correct_result:
  73         raise Exception("error in implementation:\ncorrect   = %s"
  74                          "\nold-style = %s\ngenerator = %s" %
  75                          (correct_result, oldrange_result, genrange_result))
  76     print "Timings for range(1000):"
  77     t1 = time.time()
  78     for i in oldrange(1000):
  79         pass
  80     t2 = time.time()
  81     for i in genrange(1000):
  82         pass
  83     t3 = time.time()
  84     for i in __builtin__.range(1000):
  85         pass
  86     t4 = time.time()
  87     print t2-t1, 'sec (old-style class)'
  88     print t3-t2, 'sec (generator)'
  89     print t4-t3, 'sec (built-in)'
  90
  91
  92 if __name__ == '__main__':
  93     test()