Description
First of all thanks a lot for the awesome library! I just recently discovered it and it saved me so many headaches. Recently I was trying to do something of this sort, where either x or y has to be given to the __init__ method for this to be valid:
@define
class MyClass:
x: int = field()
y: int = field()
@x.default
def y_plus_one(self):
return self.y + 1
@y.default
def x_plus_one(self):
return self.x + 1This however (as the docs state) fails because self.y would not be initialized during the call to y_plus_one. Even though the docs state this fails I wanted to try and fix the issue and managed to do so in a very hacky way. However in the process I thought up a non invasive way in which this may work.
If we first initialize those fields that were given a value through __init__ and then use the NOTHING sentinel to initialize the values for those attributes that were not initialized through __init__ but before calling the factories, the problem dissapears. The reordered __init__ method would look something like this (I'm not really sure how the method is autogenerated but its a rough idea):
@define
class MyClass:
...
def __init__(self, x = NOTHING, y = NOTHING): # <- this is autogenerated
# initialize all fields before calling factories
if x is not NOTHING:
self.x = x
elif isinstance(self.__attrs_attrs__['x'].default, Factory):
self.x = NOTHING
elif self.__attrs_attrs__['x'].default is not None:
self.x = self.__attrs_attrs__['x'].default
if y is not NOTHING:
self.y = y
elif isinstance(self.__attrs_attrs__['y'].default, Factory):
self.y = NOTHING
elif self.__attrs_attrs__['y'].default is not None:
self.y = self.__attrs_attrs__['y'].default
# call the factories for all fields that were not given a value through init
if self.x is NOTHING and isinstance(self.__attrs_attrs__['x'].default, Factory):
self.x = self.__attrs_attrs__['x'].default.factory(self)
if self.x is NOTHING:
raise ValueError("a factory may not return the NOTHING sentinel")
if self.y is NOTHING and isinstance(self.__attrs_attrs__['y'].default, Factory):
self.y = self.__attrs_attrs__['y'].default.factory(self)
if self.y is NOTHING:
raise ValueError("a factory may not return the NOTHING sentinel")
...This has the additional benefit that now I can throw more descriptive error messages during initialization, like:
...
@x.default
def y_plus_one(self):
if self.y is NOTHING:
raise ValueError("either x or y has to be initialized")
return self.y + 1
...