如何在Python中封装类时访问上下文标签？

Question

我试图从封装类中获取一个封装类的上下文，比如一个标签。一种方法是传递标签，就像我在下面演示的实例化过程中一样。你知道吗

我已经了解了日志模块如何允许您使用get\u logger函数订阅子日志，并且我希望有一个get\u context（）函数。有什么办法吗？你知道吗

如果这个标签的传递达到了一个水平，就像下面的YetAnotherClass，它看起来是可以忍受的。。。但是如果你必须把它往下传3到4级，那就是我真正想要的另一个解决方案来传递这个标签的地方。你知道吗

我应该换个角度考虑这个问题吗？下面是一些示例代码：

class RootClass(object) :
    def __init__(self) :
        self.ac = AnotherClass('root_class_context')
    def do_insert(self) :
        """ use DataTableMgr class to update table """
        self.ac.insert_to_table('field1', 'field2', 'field3')

class AnotherClass(object) :
    def __init__(self, label) :
        self.context = label
        self.dtm = DataTableMgr('arg1','arg2', 'arg3', 'arg4', self.context)

    def insert_to_table(self, field1, field2, field3) :
        """ insert args to database using DataTableMgr """
        self.dtm.insert_to_table(field1, field2, field3)


class YetAnotherClass(object) :
    def __init__(self) :
        self.dtm = DataTableMgr('arg1','arg2', 'arg3', 'arg4', 'yetanother_context')

    def do_insert(self) :
        """ use DataTableMgr class to update table """
        self.dtm.insert_to_table('field1', 'field2', 'field3')

class DataTableMgr(object) :
    """ manage insert, updates to some table """
    def __init__(self, arg1, arg2, arg3, arg4, user_id) :
        self.context = user_id

    def insert_to_table(self, field1, field2, field3) :
        """ insert fields to table, while updating user id"""
        print( "inserting...(pretending to be updating sql database)")
        print(field1, field2, field3, self.context)
        print

if __name__ == "__main__" :
    #instantiate a class once removed from the inserting class and do insert
    rc = RootClass()
    rc.do_insert()

    #instantiate a class directly accessing the class for inserting
    yac = YetAnotherClass() 
    yac.do_insert()             

    #note how the context changes       
    print                                   
    print("Notice how the context changes?  "   
        ".. is there a better way to pass around this context information?")

Answer 1

我能想到的最简单的方法就是使用继承：

class DataTableMgr(object):
    """ manage insert, updates to some table """
    def __init__(self, arg1, arg2, arg3, arg4, context):
        self.context = context

    def insert_to_table(self, field1, field2, field3):
        """ insert fields to table, while updating user id"""
        print("inserting...(pretending to be updating sql database)")
        print(field1, field2, field3, self.context)
        print

    def do_insert(self):
        """ use DataTableMgr class to update table """
        self.insert_to_table('field1', 'field2', 'field3')


class AnotherClass(DataTableMgr):
    def __init__(self, context):
        DataTableMgr.__init__(self, 'arg1', 'arg2', 'arg3', 'arg4', context)


class RootClass(AnotherClass):
    def __init__(self):
        AnotherClass.__init__(self, 'root_class_context')


class YetAnotherClass(DataTableMgr):
    def __init__(self):
        DataTableMgr.__init__(
            self, 'arg1', 'arg2', 'arg3', 'arg4', 'yetanother_context')

---

但也许您不想使用继承，因为RootClass不是DataTableMgr，而是有一个DataTableMgr。 在这种情况下，您可以考虑使用多态性将上下文传递给委托的封装对象。你知道吗

class Base(object):
    def do_insert(self):
        """ use DataTableMgr class to update table """
        self.dtm.insert_to_table('field1', 'field2', 'field3', self.context)

    def insert_to_table(self, field1, field2, field3, context):
        """ insert args to database using DataTableMgr """
        self.dtm.insert_to_table(field1, field2, field3, context)

为了促进多态性，委托对象应该可以通过self.dtm访问。因此，当调用do_insert时，委托对象self.dtm调用其insert_to_table方法。如果self.dtm是DataTableMgr实例，则调用DataTableMgr.insert_to_table。但是如果self.dtm是另一个Base实例，则调用委托的insert_to_table方法。以此类推，直到委托是DataTableMgr。你知道吗

下面是一个可运行代码的示例：

class Base(object):
    def do_insert(self):
        """ use DataTableMgr class to update table """
        self.dtm.insert_to_table('field1', 'field2', 'field3', self.context)

    def insert_to_table(self, field1, field2, field3, context):
        """ insert args to database using DataTableMgr """
        self.dtm.insert_to_table(field1, field2, field3, context)


class RootClass(Base):
    def __init__(self):
        self.context = 'root_class_context'
        self.dtm = AnotherClass()


class AnotherClass(Base):
    def __init__(self):
        self.dtm = DataTableMgr('arg1', 'arg2', 'arg3', 'arg4')


class YetAnotherClass(Base):
    def __init__(self):
        self.context = 'yetanother_context'
        self.dtm = DataTableMgr('arg1', 'arg2', 'arg3', 'arg4')


class DataTableMgr(object):
    """ manage insert, updates to some table """
    def __init__(self, arg1, arg2, arg3, arg4):
        pass

    def insert_to_table(self, field1, field2, field3, context):
        """ insert fields to table, while updating user id"""
        print("inserting...(pretending to be updating sql database)")
        print(field1, field2, field3, context)
        print

if __name__ == "__main__":
    # instantiate a class once removed from the inserting class and do insert
    rc = RootClass()
    rc.do_insert()

    # instantiate a class directly accessing the class for inserting
    yac = YetAnotherClass()
    yac.do_insert()

    # note how the context changes
    print
    print("Notice how the context changes?  "
          ".. is there a better way to pass around this context information?")