core.py 文件源码

def __new__(cls, base, *args, **kw_args):
        from sympy.utilities.misc import filldedent
        from sympy.tensor.array.ndim_array import NDimArray
        from sympy.matrices.matrices import MatrixBase

        if not args:
            raise IndexException("Indexed needs at least one index.")
        if isinstance(base, (string_types, Symbol)):
            base = IndexedBase(base)
        elif not hasattr(base, '__getitem__') and not isinstance(base, IndexedBase):
            raise TypeError(filldedent("""
                Indexed expects string, Symbol, or IndexedBase as base."""))
        args = list(map(sympify, args))
        if isinstance(base, (NDimArray, collections.Iterable, Tuple, MatrixBase)) and all([i.is_number for i in args]):
            if len(args) == 1:
                return base[args[0]]
            else:
                return base[args]

        return Expr.__new__(cls, base, *args, **kw_args)