def free_symbols(self):
"""Return from the atoms of self those which are free symbols.
For most expressions, all symbols are free symbols. For some classes
this is not true. e.g. Integrals use Symbols for the dummy variables
which are bound variables, so Integral has a method to return all symbols
except those. Derivative keeps track of symbols with respect to which it
will perform a derivative; those are bound variables, too, so it has
its own symbols method.
Any other method that uses bound variables should implement a symbols
method."""
union = set.union
return reduce(union, [arg.free_symbols for arg in self.args], set())
def free_symbols(self):
"""Return from the atoms of self those which are free symbols.
For most expressions, all symbols are free symbols. For some classes
this is not true. e.g. Integrals use Symbols for the dummy variables
which are bound variables, so Integral has a method to return all symbols
except those. Derivative keeps track of symbols with respect to which it
will perform a derivative; those are bound variables, too, so it has
its own symbols method.
Any other method that uses bound variables should implement a symbols
method."""
union = set.union
return reduce(union, [arg.free_symbols for arg in self.args], set())