def _e(op, inv=False):
def inner(self, rhs):<EOL><INDENT>if inv:<EOL><INDENT>return Expression(rhs, op, self)<EOL><DEDENT>return Expression(self, op, rhs)<EOL><DEDENT>return inner<EOL>
Lightweight factory which returns a method that builds an Expression
consisting of the left-hand and right-hand operands, using `op`.