Initial revision

Demo/classes/Range.py

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+# Example of a generator: re-implement the built-in range function
+# without actually constructing the list of values.  (It turns out
+# that the built-in function is about 20 times faster -- that's why
+# it's built-in. :-)
+
+
+# Wrapper function to emulate the complicated range() arguments
+
+def range(*a):
+	if len(a) == 1:
+		start, stop, step = 0, a[0], 1
+	elif len(a) == 2:
+		start, stop = a
+		step = 1
+	elif len(a) == 3:
+		start, stop, step = a
+	else:
+		raise TypeError, 'range() needs 1-3 arguments'
+	return Range().init(start, stop, step)
+	
+
+# Class implementing a range object.
+# To the user the instances feel like immutable sequences
+# (and you can't concatenate or slice them)
+
+class Range:
+
+	# initialization -- should be called only by range() above
+	def init(self, start, stop, step):
+		if step == 0:
+			raise ValueError, 'range() called with zero step'
+		self.start = start
+		self.stop = stop
+		self.step = step
+		self.len = max(0, int((self.stop - self.start) / self.step))
+		return self
+
+	# implement `x` and is also used by print x
+	def __repr__(self):
+		return 'range' + `self.start, self.stop, self.step`
+
+	# implement len(x)
+	def __len__(self):
+		return self.len
+
+	# implement x[i]
+	def __getitem__(self, i):
+		if 0 <= i < self.len:
+			return self.start + self.step * i
+		else:
+			raise IndexError, 'range[i] index out of range'
+
+
+# Small test program
+
+def test():
+	import time, builtin
+	print range(10), range(-10, 10), range(0, 10, 2)
+	for i in range(100, -100, -10): print i,
+	print
+	t1 = time.millitimer()
+	for i in range(1000):
+		pass
+	t2 = time.millitimer()
+	for i in builtin.range(1000):
+		pass
+	t3 = time.millitimer()
+	print t2-t1, 'msec (class)'
+	print t3-t2, 'msec (built-in)'
+
+
+test()