code: def is_between(self, low, high):
          
          val_type = type(self.val)
          self._validate_between_args(val_type, low, high)
  
          if self.val < low or self.val > high:
              if val_type is datetime.datetime:
                  self._err('Expected <%s> to be between <%s> and <%s>, but was not.' % (self.val.strftime('%Y-%m-%d %H:%M:%S'), low.strftime('%Y-%m-%d %H:%M:%S'), high.strftime('%Y-%m-%d %H:%M:%S')))
              else:
                  self._err('Expected <%s> to be between <%s> and <%s>, but was not.' % (self.val, low, high))
          return self
docs: Asserts that val is numeric and is between low and high.