Iterator and Generator version of python range function

I have created iterator and generator version of python range function

Here is Generator version:

def irange(*args):
 if len(args) > 3:
     raise TypeError('irange() expected at most 3 arguments, got %s' % (len(args)))
 elif len(args) == 1:
     start_element = 0
     end_element = args[0]
     step = 1
 else:
     start_element = args[0]
     end_element = args[1]
     if len(args) == 2:
         step = 1
     elif (args[2] % 1 == 0 and args[2] != 0):
         step = args[2]
     else:
         raise ValueError('irange() step argument must not be zero')

 if((type(start_element) is str) or (type(end_element) is str) 
    or (type(step) is str)):
     raise TypeError('irange() integer expected, got str')

 count = 0
 while (( start_element + step < end_element ) 
        if 0 < step else 
        ( end_element < start_element + step )) :
     if count == 0:
         item = start_element
     else:
         item = start_element + step
     start_element = item
     count +=1
     yield item

Here is Iterator veersion:

class Irange:
 def __init__(self, start_element, end_element=None, step=1):
     if step == 0:
         raise ValueError('Irange() step argument must not be zero')
     if((type(start_element) is str) or (type(end_element) is str) 
        or (type(step) is str)):
         raise TypeError('Irange() integer expected, got str')

     self.start_element = start_element
     self.end_element = end_element
     self.step = step
     self.index = 0

     if end_element is None:
        self.start_element = 0
        self.end_element = start_element

 def __iter__(self):
     return self

 def next(self):
     if self.index == 0:
         self.item = self.start_element
     else:
         self.item = self.start_element + self.step
     if self.step > 0:
         if self.item >= self.end_element:
                raise StopIteration
     elif self.step < 0:
         if self.item <= self.end_element:
             raise StopIteration

     self.start_element = self.item
     self.index += 1
     return self.item

Usage:

 >>> for i in irange(2,5):
 ...  print i,
 2 3 4
 >>> for i in irange(2,-3,-1):
 ...  print i,
 2 1 0 -1 -2
 >>> for i in Irange(3):
 ...  print i,
 0 1 2

would like to know if the approach is correct.