trace.py 文件源码

def __new__(cls, *args):
        """ Construct a Trace object.

        Parameters
        ==========
        args = sympy expression
        indices = tuple/list if indices, optional

        """

        # expect no indices,int or a tuple/list/Tuple
        if (len(args) == 2):
            if not isinstance(args[1], (list, Tuple, tuple)):
                indices = Tuple(args[1])
            else:
                indices = Tuple(*args[1])

            expr = args[0]
        elif (len(args) == 1):
            indices = Tuple()
            expr = args[0]
        else:
            raise ValueError("Arguments to Tr should be of form "
                             "(expr[, [indices]])")

        if isinstance(expr, Matrix):
            return expr.trace()
        elif hasattr(expr, 'trace') and callable(expr.trace):
            #for any objects that have trace() defined e.g numpy
            return expr.trace()
        elif isinstance(expr, Add):
            return Add(*[Tr(arg, indices) for arg in expr.args])
        elif isinstance(expr, Mul):
            c_part, nc_part = expr.args_cnc()
            if len(nc_part) == 0:
                return Mul(*c_part)
            else:
                obj = Expr.__new__(cls, Mul(*nc_part), indices )
                #this check is needed to prevent cached instances
                #being returned even if len(c_part)==0
                return Mul(*c_part)*obj if len(c_part) > 0 else obj
        elif isinstance(expr, Pow):
            if (_is_scalar(expr.args[0]) and
                    _is_scalar(expr.args[1])):
                return expr
            else:
                return Expr.__new__(cls, expr, indices)
        else:
            if (_is_scalar(expr)):
                return expr

            return Expr.__new__(cls, expr, indices)