def is_math(value):
    """must be a valid math operator"""
    valid_maths = ['__add__', '__radd__', '__sub__', '__rsub__', '__mul__',
        '__rmul__', '__div__', '__rdiv__']
    valid_maths += ['sin', 'cos', 'tan']
    valid_maths += ['__and__', '__or__']
    return value in valid_maths, value
