让我们考虑 python (3.x) 脚本:
主要.py:
from test.team import team
from test.user import user
if __name__ == '__main__':
u = user()
t = team()
u.setTeam(t)
t.setLeader(u)
测试/用户.py:
from test.team import team
class user:
def setTeam(self, t):
if issubclass(t, team.__class__):
self.team = t
测试/团队.py:
from test.user import user
class team:
def setLeader(self, u):
if issubclass(u, user.__class__):
self.leader = u
现在,当然,我有循环导入和出色的 ImportError。
所以,不是pythonista,我有三个问题。首先:
一世。我怎样才能使这件事起作用?
而且,知道有人不可避免地会说“循环导入总是表明设计问题”,第二个问题来了:
ii. 为什么这个设计不好?
最后,第三个:
iii. 有什么更好的选择?
准确地说,上面的类型检查只是一个例子,还有一个基于类的索引层,它允许ie。找到所有用户都是一个团队的成员(用户类有许多子类,因此索引加倍,对于一般用户和每个特定子类)或所有团队都有给定用户作为成员
编辑:
我希望更详细的示例将阐明我试图实现的目标。为了便于阅读而省略了文件(但是有一个 300kb 的源文件让我感到害怕,所以请假设每个类都在不同的文件中)
# ENTITY
class Entity:
_id = None
_defs = {}
_data = None
def __init__(self, **kwargs):
self._id = uuid.uuid4() # for example. or randint(). or x+1.
self._data = {}.update(kwargs)
def __settattr__(self, name, value):
if name in self._defs:
if issubclass(value.__class__, self._defs[name]):
self._data[name] = value
# more stuff goes here, specially indexing dependencies, so we can
# do Index(some_class, name_of_property, some.object) to find all
# objects of some_class or its children where
# given property == some.object
else:
raise Exception('Some misleading message')
else:
self.__dict__[name] = value
def __gettattr__(self, name):
return self._data[name]
# USERS
class User(Entity):
_defs = {'team':Team}
class DPLUser(User):
_defs = {'team':DPLTeam}
class PythonUser(DPLUser)
pass
class PerlUser(DPLUser)
pass
class FunctionalUser(User):
_defs = {'team':FunctionalTeam}
class HaskellUser(FunctionalUser)
pass
class ErlangUser(FunctionalUser)
pass
# TEAMS
class Team(Entity):
_defs = {'leader':User}
class DPLTeam(Team):
_defs = {'leader':DPLUser}
class FunctionalTeam(Team):
_defs = {'leader':FunctionalUser}
现在有一些用法:
t1 = FunctionalTeam()
t2 = DLPTeam()
t3 = Team()
u1 = HaskellUser()
u2 = PythonUser()
t1.leader = u1 # ok
t2.leader = u2 # ok
t1.leader = u2 # not ok, exception
t3.leader = u2 # ok
# now , index
print(Index(FunctionalTeam, 'leader', u2)) # -> [t2]
print(Index(Team, 'leader', u2)) # -> [t2,t3]
所以,除了这个邪恶的循环导入之外,它工作得很好(省略了实现细节,但没有什么复杂的)。