I'm writing two classes, Parent and Child, so that the parent contains several children and each child contains a reference to the parent to eventually invoke its method(). Since I use type hinting (PIP 484, mainly for clarity and readability of the code), I come up with the error:
ValueError: Circular reference detected
due to the fact that example/child.py imports Parent already defined in example/parent.py. Does anyone know how to get rid of this error?
My Parent (in example/parent.py) is as follows:
from typing import List
from example.child import Child
class Parent(object):
def __init__(self, children: List[Child] = None) -> None:
self._children = \
{child.name: child for child in children} if children else {}
@property
def children(self) -> List[Child]:
return list(self._children.values())
@children.setter
def children(self, value: List[Child] = None) -> None:
self._children = {child.name: child for child in value} if value else {}
def new_child(self, name: str) -> Child:
child = Child(self, name)
self._children[name] = child
return child
def method(self) -> bool:
return len(self._children) % 2 == 0
My Child (in example/child.py), instead, is as follows:
from typing import TYPE_CHECKING, List
if TYPE_CHECKING:
from example.parent import Parent
class Child(object):
def __init__(self, parent: 'Parent', name: str) -> None:
if parent is None:
raise ValueError("'parent' is invalid: <%s>" % parent)
if name is None or not str(name).strip():
raise ValueError("'name' is invalid: <%s>" % name)
self._parent = parent
self._name = str(name).strip()
@property
def parent(self) -> 'Parent':
return self._parent
@property
def name(self) -> str:
return self._name
def method(self) -> None:
print('we are even' if self._parent.method() else 'we are odd')
Notice that I already introduced the trick which consists in using the TYPE_CHECKING variable, but in this case it doesn't help. Thanks in advance!
