Add code for a range function that uses generators.

Cleaned up existing code by abstracting code to parse arguments.  Also removed
any unneeded operations (such as calling 'int' on a division when using floor
division also works).  Fixed a bug where the values  returned by
OldStyleRange could be short by one value.  Added more documentation.

Testing code also has a basic sanity check.

Demo/classes/Range.py

@@ -1,71 +1,93 @@
-# 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. :-)
+"""Example of a generator: re-implement the built-in range function
+without actually constructing the list of values.
 
+OldStyleRange is coded in the way required to work in a 'for' loop before
+iterators were introduced into the language; using __getitem__ and __len__ .
 
-# 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
+"""
+def handleargs(arglist):
+    """Take list of arguments and extract/create proper start, stop, and step
+    values and return in a tuple"""
+    try:
+        if len(arglist) == 1:
+            return 0, int(arglist[0]), 1
+        elif len(arglist) == 2:
+            return int(arglist[0]), int(arglist[1]), 1
+        elif len(arglist) == 3:
+            if arglist[2] == 0:
+                raise ValueError("step argument must not be zero")
+            return tuple(int(x) for x in arglist)
         else:
-        raise TypeError, 'range() needs 1-3 arguments'
-    return Range(start, stop, step)
+            raise TypeError("range() accepts 1-3 arguments, given", len(arglist))
+    except TypeError:
+        raise TypeError("range() arguments must be numbers or strings "
+        "representing numbers")
 
+def genrange(*a):
+    """Function to implement 'range' as a generator"""
+    start, stop, step = handleargs(a)
+    value = start
+    while value < stop:
+        yield value
+        value += step
 
-# Class implementing a range object.
-# To the user the instances feel like immutable sequences
-# (and you can't concatenate or slice them)
+class oldrange:
+    """Class implementing a range object.
+    To the user the instances feel like immutable sequences
+    (and you can't concatenate or slice them)
 
-class Range:
+    Done using the old way (pre-iterators; __len__ and __getitem__) to have an
+    object be used by a 'for' loop.
 
-    # 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))
+    """
+
+    def __init__(self, *a):
+        """ Initialize start, stop, and step values along with calculating the
+        nubmer of values (what __len__ will return) in the range"""
+        self.start, self.stop, self.step = handleargs(a)
+        self.len = max(0, (self.stop - self.start) // self.step)
 
-    # implement repr(x) and is also used by print x
     def __repr__(self):
+        """implement repr(x) which is also used by print"""
         return 'range(%r, %r, %r)' % (self.start, self.stop, self.step)
 
-    # implement len(x)
     def __len__(self):
+        """implement len(x)"""
         return self.len
 
-    # implement x[i]
     def __getitem__(self, i):
-        if 0 <= i < self.len:
+        """implement x[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
+    #Just a quick sanity check
+    correct_result = __builtin__.range(5, 100, 3)
+    oldrange_result = list(oldrange(5, 100, 3))
+    genrange_result = list(genrange(5, 100, 3))
+    if genrange_result != correct_result or oldrange_result != correct_result:
+        raise Exception("error in implementation:\ncorrect   = %s"
+                         "\nold-style = %s\ngenerator = %s" %
+                         (correct_result, oldrange_result, genrange_result))
+    print "Timings for range(1000):"
     t1 = time.time()
-    for i in range(1000):
+    for i in oldrange(1000):
         pass
     t2 = time.time()
-    for i in __builtin__.range(1000):
+    for i in genrange(1000):
         pass
     t3 = time.time()
-    print t2-t1, 'sec (class)'
-    print t3-t2, 'sec (built-in)'
+    for i in __builtin__.range(1000):
+        pass
+    t4 = time.time()
+    print t2-t1, 'sec (old-style class)'
+    print t3-t2, 'sec (generator)'
+    print t4-t3, 'sec (built-in)'
 
 
+if __name__ == '__main__':
     test()