Add @as_model decorator (#268)

Co-authored-by: Rob Zinkov <8529+zaxtax@users.noreply.github.com>

docs/api_reference.rst

@@ -8,7 +8,8 @@ methods in the current release of PyMC experimental.
 .. autosummary::
    :toctree: generated/
 
-   marginal_model.MarginalModel
+   as_model
+   MarginalModel
    model_builder.ModelBuilder
 
 Inference

pymc_experimental/__init__.py

@@ -25,4 +25,5 @@
 
 from pymc_experimental import distributions, gp, utils
 from pymc_experimental.inference.fit import fit
-from pymc_experimental.marginal_model import MarginalModel
+from pymc_experimental.model.marginal_model import MarginalModel
+from pymc_experimental.model.model_api import as_model

pymc_experimental/model/model_api.py

@@ -0,0 +1,46 @@
+from functools import wraps
+
+from pymc import Model
+
+
+def as_model(*model_args, **model_kwargs):
+    R"""
+    Decorator to provide context to PyMC models declared in a function.
+    This removes all need to think about context managers and lets you separate creating a generative model from using the model.
+
+    Adapted from `Rob Zinkov's blog post <https://www.zinkov.com/posts/2023-alternative-frontends-pymc/>`_ and inspired by the `sampled <https://github.com/colcarroll/sampled>`_ decorator for PyMC3.
+
+    Examples
+    --------
+    .. code:: python
+
+        import pymc as pm
+        import pymc_experimental as pmx
+
+        # The following are equivalent
+
+        # standard PyMC API with context manager
+        with pm.Model(coords={"obs": ["a", "b"]}) as model:
+            x = pm.Normal("x", 0., 1., dims="obs")
+            pm.sample()
+
+        # functional API using decorator
+        @pmx.as_model(coords={"obs": ["a", "b"]})
+        def basic_model():
+            pm.Normal("x", 0., 1., dims="obs")
+
+        m = basic_model()
+        pm.sample(model=m)
+
+    """
+
+    def decorator(f):
+        @wraps(f)
+        def make_model(*args, **kwargs):
+            with Model(*model_args, **model_kwargs) as m:
+                f(*args, **kwargs)
+            return m
+
+        return make_model
+
+    return decorator

pymc_experimental/tests/test_marginal_model.py → pymc_experimental/tests/model/test_marginal_model.py

@@ -12,7 +12,7 @@
 from pymc.util import UNSET
 from scipy.special import logsumexp
 
-from pymc_experimental.marginal_model import (
+from pymc_experimental.model.marginal_model import (
     FiniteDiscreteMarginalRV,
     MarginalModel,
     is_conditional_dependent,

pymc_experimental/tests/model/test_model_api.py

@@ -0,0 +1,22 @@
+import numpy as np
+import pymc as pm
+
+import pymc_experimental as pmx
+
+
+def test_logp():
+    """Compare standard PyMC `with pm.Model()` context API against `pmx.model` decorator
+    and a functional syntax. Checks whether the kwarg `coords` can be passed.
+    """
+    coords = {"obs": ["a", "b"]}
+
+    with pm.Model(coords=coords) as model:
+        pm.Normal("x", 0.0, 1.0, dims="obs")
+
+    @pmx.as_model(coords=coords)
+    def model_wrapped():
+        pm.Normal("x", 0.0, 1.0, dims="obs")
+
+    mw = model_wrapped()
+
+    np.testing.assert_equal(model.point_logps(), mw.point_logps())