Demo/classes/Range.py

   1 # Example of a generator: re-implement the built-in range function
   2 # without actually constructing the list of values.  (It turns out
   3 # that the built-in function is about 20 times faster -- that's why
   4 # it's built-in. :-)
   5
   6
   7 # Wrapper function to emulate the complicated range() arguments
   8
   9 def range(*a):
  10         if len(a) == 1:
  11                 start, stop, step = 0, a[0], 1
  12         elif len(a) == 2:
  13                 start, stop = a
  14                 step = 1
  15         elif len(a) == 3:
  16                 start, stop, step = a
  17         else:
  18                 raise TypeError, 'range() needs 1-3 arguments'
  19         return Range(start, stop, step)
  20
  21
  22 # Class implementing a range object.
  23 # To the user the instances feel like immutable sequences
  24 # (and you can't concatenate or slice them)
  25
  26 class Range:
  27
  28         # initialization -- should be called only by range() above
  29         def __init__(self, start, stop, step):
  30                 if step == 0:
  31                         raise ValueError, 'range() called with zero step'
  32                 self.start = start
  33                 self.stop = stop
  34                 self.step = step
  35                 self.len = max(0, int((self.stop - self.start) / self.step))
  36
  37         # implement `x` and is also used by print x
  38         def __repr__(self):
  39                 return 'range' + `self.start, self.stop, self.step`
  40
  41         # implement len(x)
  42         def __len__(self):
  43                 return self.len
  44
  45         # implement x[i]
  46         def __getitem__(self, i):
  47                 if 0 <= i < self.len:
  48                         return self.start + self.step * i
  49                 else:
  50                         raise IndexError, 'range[i] index out of range'
  51
  52
  53 # Small test program
  54
  55 def test():
  56         import time, __builtin__
  57         print range(10), range(-10, 10), range(0, 10, 2)
  58         for i in range(100, -100, -10): print i,
  59         print
  60         t1 = time.time()
  61         for i in range(1000):
  62                 pass
  63         t2 = time.time()
  64         for i in __builtin__.range(1000):
  65                 pass
  66         t3 = time.time()
  67         print t2-t1, 'sec (class)'
  68         print t3-t2, 'sec (built-in)'
  69
  70
  71 test()