pymc.Model 的示例子类中的 super().__init__() 中的模型参数是什么？

Question

pymc.Model

文档显示此示例：

class CustomModel(Model):
    # 1) override init
    def __init__(self, mean=0, sigma=1, name=''):
        # 2) call super's init first, passing model and name
        # to it name will be prefix for all variables here if
        # no name specified for model there will be no prefix
        super().__init__(name, model)
        # now you are in the context of instance,
        # `modelcontext` will return self you can define
        # variables in several ways note, that all variables
        # will get model's name prefix

        # 3) you can create variables with the register_rv method
        self.register_rv(Normal.dist(mu=mean, sigma=sigma), 'v1', initval=1)
        # this will create variable named like '{name::}v1'
        # and assign attribute 'v1' to instance created
        # variable can be accessed with self.v1 or self['v1']

        # 4) this syntax will also work as we are in the
        # context of instance itself, names are given as usual
        Normal('v2', mu=mean, sigma=sigma)

        # something more complex is allowed, too
        half_cauchy = HalfCauchy('sigma', beta=10, initval=1.)
        Normal('v3', mu=mean, sigma=half_cauchy)

        # Deterministic variables can be used in usual way
        Deterministic('v3_sq', self.v3 ** 2)

        # Potentials too
        Potential('p1', pt.constant(1))

# After defining a class CustomModel you can use it in several
# ways

# I:
#   state the model within a context
with Model() as model:
    CustomModel()
    # arbitrary actions

# II:
#   use new class as entering point in context
with CustomModel() as model:
    Normal('new_normal_var', mu=1, sigma=0)

# III:
#   just get model instance with all that was defined in it
model = CustomModel()

# IV:
#   use many custom models within one context
with Model() as model:
    CustomModel(mean=1, name='first')
    CustomModel(mean=2, name='second')

# variables inside both scopes will be named like `first::*`, `second::*`

显然这不是一个工作示例，而是旨在概述定义自定义 PyMC 模型类的一些内部结构。

我确实对这个例子的一部分有疑问。当父类用

super().__init__(name, model)

初始化时，我看到传递了两个参数：

name

和

model

。我认为

name

可能只是一个字符串，但我不太清楚的是

model

应该是什么。

model

也应该是一个字符串吗？还是别的？

Answer 1

从您链接的文档中，

model

似乎是一个模块级变量，由上下文管理器设置：

with Model() as model:  # the "as model" part, here
    CustomModel()

我不知道为什么要使用上下文管理器，但就像这样做：

class Bar:
    def __init__(self):
        self.value = model


# just to demonstrate & FYI
try:
    Bar()  # will raise that "model" is undefined
except NameError as ex:
    print(ex)


# entering the contextmanager
model = Model()  # the "as model"
model.__enter__()

try:
    bar = Bar()  # doesn't raise this time
except Exception as ex:
    # exiting the contextmanager that errored
    model.__exit__(type(err), err, err.__traceback__)
else:
    # exiting the contextmanager without an error
    model.__exit__(None, None, None)


assert bar.value is model  # True

换句话说，在那个例子中，

model

是

Model()

。

IMO 代码确实令人困惑，如果它作为显式构造函数 arg 传入，则不会那么混乱。