Returns a sliced DataFrame

		Parameters
		----------
			slice : tuple(from,to)
				from : str
				to : str
					States the 'from' and 'to' values which 
					will get rendered as df.ix[from:to]
			df : DataFrame
				If omitted then the QuantFigure.DataFrame is resampled.

def _get_sliced(self,slice,df=None):
		"""
		Returns a sliced DataFrame

		Parameters
		----------
			slice : tuple(from,to)
				from : str
				to : str
					States the 'from' and 'to' values which 
					will get rendered as df.ix[from:to]
			df : DataFrame
				If omitted then the QuantFigure.DataFrame is resampled.
		"""

		df=self.df.copy() if df==None else df
		if type(slice) not in (list,tuple):
			raise Exception('Slice must be a tuple two values')
		if len(slice)!=2:
			raise Exception('Slice must be a tuple two values')
		a,b=slice
		a=None if a in ('',None) else utils.make_string(a)
		b=None if b in ('',None) else utils.make_string(b)
		return df.ix[a:b]