add.py 文件源码

def _combine_inverse(lhs, rhs):
        """
        Returns lhs - rhs, but treats arguments like symbols, so things like
        oo - oo return 0, instead of a nan.
        """
        from sympy import oo, I, expand_mul
        if lhs == oo and rhs == oo or lhs == oo*I and rhs == oo*I:
            return S.Zero
        return expand_mul(lhs - rhs)