docs: def xfrange(start, stop=None, step=1):
  	"""
  	Iterate through an arithmetic progression.
  
  	:param start: Starting number.
  	:type start: float, int, long
  	:param stop: Stopping number.
  	:type stop: float, int, long
  	:param step: Stepping size.
  	:type step: float, int, long
  	"""
  	if stop is None:
  		stop = start
  		start = 0.0
  	start = float(start)
  	while start < stop:
  		yield start
  		start += step