def _depending_columns(self, ds):
        '''Find all columns that this selection depends on for df ds'''
        depending = set()
        for expression in self.expressions:
            expression = ds._expr(expression)  # make sure it is an expression
            depending |= expression.variables()
        if self.previous_selection:
            depending |= self.previous_selection._depending_columns(ds)
        return depending
def _depending_columns(self, ds):
        
        depending = set()
        for expression in self.expressions:
            expression = ds._expr(expression)  
            depending |= expression.variables()
        if self.previous_selection:
            depending |= self.previous_selection._depending_columns(ds)
        return depending
def _depending_columns ( self , ds ) : depending = set ( ) for expression in self . expressions : expression = ds . _expr ( expression ) # make sure it is an expression depending |= expression . variables ( ) if self . previous_selection : depending |= self . previous_selection . _depending_columns ( ds ) return depending
Find all columns that this selection depends on for df ds
Find all columns that this selection depends on for df ds