#NEWLINE# @ property #NEWLINE# def free_symbols( self ) : #NEWLINE# #INDENT# '\n        This method returns the symbols in the object, excluding those\n        that take on a specific value (i.e. the dummy symbols).\n\n        Examples\n        ========\n\n        >>> from sympy import Sum\n        >>> from sympy.abc import x, y\n        >>> Sum(x, (x, y, 1)).free_symbols\n        set([y])\n        ' #NEWLINE# ( function , limits ) = ( self . function , self . limits ) #NEWLINE# isyms = function . free_symbols #NEWLINE# for xab in limits : #NEWLINE# #INDENT# if ( len ( xab ) == 1 ) : #NEWLINE# #INDENT# isyms . add ( xab [ 0 ] ) #NEWLINE# continue #NEWLINE# #UNINDENT# if ( xab [ 0 ] in isyms ) : #NEWLINE# #INDENT# isyms . remove ( xab [ 0 ] ) #NEWLINE# #UNINDENT# for i in xab [ 1 : ] : #NEWLINE# #INDENT# isyms . update ( i . free_symbols ) #NEWLINE# #UNINDENT# #UNINDENT# return isyms