getattr_static.py 文件源码

def getattr_static(obj, attr, default=_sentinel):
    """Retrieve attributes without triggering dynamic lookup via the
       descriptor protocol,  __getattr__ or __getattribute__.

       Note: this function may not be able to retrieve all attributes
       that getattr can fetch (like dynamically created attributes)
       and may find attributes that getattr can't (like descriptors
       that raise AttributeError). It can also return descriptor objects
       instead of instance members in some cases. See the
       documentation for details.

       Returns a tuple `(attr, is_get_descriptor)`. is_get_descripter means that
       the attribute is a descriptor that has a `__get__` attribute.
    """
    instance_result = _sentinel
    if not _is_type(obj):
        klass = _get_type(obj)
        dict_attr = _shadowed_dict(klass)
        if (dict_attr is _sentinel or
            type(dict_attr) is types.MemberDescriptorType):
            instance_result = _check_instance(obj, attr)
    else:
        klass = obj

    klass_result = _check_class(klass, attr)

    if instance_result is not _sentinel and klass_result is not _sentinel:
        if _safe_hasattr(klass_result, '__get__') \
                and _safe_is_data_descriptor(klass_result):
            # A get/set descriptor has priority over everything.
            return klass_result, True

    if instance_result is not _sentinel:
        return instance_result, False
    if klass_result is not _sentinel:
        return klass_result, _safe_hasattr(klass_result, '__get__')

    if obj is klass:
        # for types we check the metaclass too
        for entry in _static_getmro(type(klass)):
            if _shadowed_dict(type(entry)) is _sentinel:
                try:
                    return entry.__dict__[attr], False
                except KeyError:
                    pass
    if default is not _sentinel:
        return default, False
    raise AttributeError(attr)