当通过传递的对象调用不同的方法时,使用 isinstance 是否合理

Is usage of isinstance is justified when calling different methods by passed object

我正在开发能够读取文件低级数据(即映射等)并将结果存储到 sqlite DB 的小工具,使用 python 的内置 sqlite API。

对于解析的文件数据,我有 3 classes:

class GenericFile: # general file class 
    # bunch of methods here
    ...
class SomeFileObject_A: # low level class for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...
class SomeFileObject_B: # low level cass for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...

sqlite 接口实现为单独的 class:

class Database:
    def insert(self, object_to_insert):
    ...
    def _insert_generic_file_object(self, object_to_insert):
    ...
    def _insert_file_object_a(self, object_to_insert):
    ...
    def _insert_file_object_b(self, object_to_insert):
    ...
    # bunch of sqlite related methods

当我需要向数据库中插入一些对象时,我正在使用 db.insert(object)

现在我认为在我的 insert 方法中使用 isinstance 可能是个好主意,因为它会处理任何插入的对象,而无需为每个对象显式调用合适的方法,看起来更优雅。 但是在看了更多isinstance之后,我开始怀疑,我的设计不是很好。

下面是通用 insert 方法的实现:

class Database:
    def insert(self, object_to_insert):
        self._logger.info("inserting %s object", object_to_insert.__class__.__name__)
        if isinstance(object_to_insert, GenericFile):
            self._insert_generic_file_object(object_to_insert)
        elif isinstance(object_to_insert, SomeFileObject_A):
            self._insert_file_object_a(object_to_insert)
        elif isinstance(object_to_insert, SomeFileObject_B):
            self._insert_file_object_b(object_to_insert)
        else:
            self._logger.error("Insert Failed. Bad object type %s" % type(object_to_insert))
            raise Exception
        self._db_connection.commit()

那么,在我的情况下是否应该避免 isinstace,如果应该,这里有什么更好的解决方案?

谢谢

OO 的基本原则之一是用多态分派替换显式开关。在您的情况下,解决方案是使用双重分派,因此 FileObect 有责任知道要调用哪个 Database 方法,即:

class GenericFile: # general file class 
    # bunch of methods here
    ...
    def insert(self, db):
        return db.insert_generic_file_object(self)


class SomeFileObject_A: # low level class for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...
    def insert(self, db):
        return db.insert_file_object_a(self)


class SomeFileObject_B: # low level cass for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...
    def insert(self, db):
        return db.insert_file_object_b(self)


class Database:
    def insert(self, obj):
        return obj.insert(self)