Add option to save model graph to an image

pymc/model/core.py

@@ -1833,7 +1833,13 @@ def debug_parameters(rv):
             print_("You can set `verbose=True` for more details")
 
     def to_graphviz(
-        self, *, var_names: Optional[Iterable[VarName]] = None, formatting: str = "plain"
+        self,
+        *,
+        var_names: Optional[Iterable[VarName]] = None,
+        formatting: str = "plain",
+        save: Optional[str] = None,
+        figsize: Optional[tuple[int, int]] = None,
+        dpi: int = 300,
     ):
         """Produce a graphviz Digraph from a PyMC model.
 
@@ -1851,6 +1857,14 @@ def to_graphviz(
             Subset of variables to be plotted that identify a subgraph with respect to the entire model graph
         formatting : str, optional
             one of { "plain" }
+        save : str, optional
+            If provided, an image of the graph will be saved to this location. The format is inferred from
+            the file extension.
+        figsize : tuple[int, int], optional
+            Width and height of the figure in inches. If not provided, uses the default figure size. It only affect
+            the size of the saved figure.
+        dpi : int, optional
+            Dots per inch. It only affects the resolution of the saved figure. The default is 300.
 
         Examples
         --------
@@ -1877,7 +1891,14 @@ def to_graphviz(
 
             schools.to_graphviz()
         """
-        return model_to_graphviz(model=self, var_names=var_names, formatting=formatting)
+        return model_to_graphviz(
+            model=self,
+            var_names=var_names,
+            formatting=formatting,
+            save=save,
+            figsize=figsize,
+            dpi=dpi,
+        )
 
 
 # this is really disgusting, but it breaks a self-loop: I can't pass Model

pymc/model_graph.py

@@ -15,6 +15,7 @@
 
 from collections import defaultdict
 from collections.abc import Iterable, Sequence
+from os import path
 from typing import Optional
 
 from pytensor import function
@@ -238,7 +239,14 @@ def get_plates(self, var_names: Optional[Iterable[VarName]] = None) -> dict[str,
 
         return dict(plates)
 
-    def make_graph(self, var_names: Optional[Iterable[VarName]] = None, formatting: str = "plain"):
+    def make_graph(
+        self,
+        var_names: Optional[Iterable[VarName]] = None,
+        formatting: str = "plain",
+        save=None,
+        figsize=None,
+        dpi=300,
+    ):
         """Make graphviz Digraph of PyMC model
 
         Returns
@@ -271,6 +279,18 @@ def make_graph(self, var_names: Optional[Iterable[VarName]] = None, formatting:
             for parent in parents:
                 graph.edge(parent.replace(":", "&"), child.replace(":", "&"))
 
+        if save is not None:
+            width, height = (None, None) if figsize is None else figsize
+            base, ext = path.splitext(save)
+            if ext:
+                ext = ext.replace(".", "")
+            else:
+                ext = "png"
+            graph_c = graph.copy()
+            graph_c.graph_attr.update(size=f"{width},{height}!")
+            graph_c.graph_attr.update(dpi=str(dpi))
+            graph_c.render(filename=base, format=ext, cleanup=True)
+
         return graph
 
     def make_networkx(
@@ -399,6 +419,9 @@ def model_to_graphviz(
     *,
     var_names: Optional[Iterable[VarName]] = None,
     formatting: str = "plain",
+    save: Optional[str] = None,
+    figsize: Optional[tuple[int, int]] = None,
+    dpi: int = 300,
 ):
     """Produce a graphviz Digraph from a PyMC model.
 
@@ -418,6 +441,14 @@ def model_to_graphviz(
         Subset of variables to be plotted that identify a subgraph with respect to the entire model graph
     formatting : str, optional
         one of { "plain" }
+    save : str, optional
+        If provided, an image of the graph will be saved to this location. The format is inferred from
+        the file extension.
+    figsize : tuple[int, int], optional
+        Width and height of the figure in inches. If not provided, uses the default figure size. It only affect
+        the size of the saved figure.
+    dpi : int, optional
+        Dots per inch. It only affects the resolution of the saved figure. The default is 300.
 
     Examples
     --------
@@ -453,4 +484,10 @@ def model_to_graphviz(
             stacklevel=2,
         )
     model = pm.modelcontext(model)
-    return ModelGraph(model).make_graph(var_names=var_names, formatting=formatting)
+    return ModelGraph(model).make_graph(
+        var_names=var_names,
+        formatting=formatting,
+        save=save,
+        figsize=figsize,
+        dpi=dpi,
+    )

tests/model/test_core.py

@@ -1690,10 +1690,20 @@ def school_model(J: int) -> pm.Model:
     @pytest.mark.parametrize(
         argnames="var_names", argvalues=[None, ["mu", "tau"]], ids=["all", "subset"]
     )
-    def test_graphviz_call_function(self, var_names) -> None:
+    @pytest.mark.parametrize(
+        argnames="filenames",
+        argvalues=["model.png", "model"],
+        ids=["ext", "no_ext"],
+    )
+    def test_graphviz_call_function(self, var_names, filenames) -> None:
         model = self.school_model(J=8)
         with patch("pymc.model.core.model_to_graphviz") as mock_model_to_graphviz:
-            model.to_graphviz(var_names=var_names)
+            model.to_graphviz(var_names=var_names, save=filenames)
             mock_model_to_graphviz.assert_called_once_with(
-                model=model, var_names=var_names, formatting="plain"
+                model=model,
+                var_names=var_names,
+                formatting="plain",
+                save=filenames,
+                figsize=None,
+                dpi=300,
             )

tests/test_data.py

@@ -16,6 +16,8 @@
 import itertools as it
 import re
 
+from os import path
+
 import cloudpickle
 import numpy as np
 import pytensor
@@ -268,7 +270,7 @@ def test_set_data_to_non_data_container_variables(self):
         error.match("The variable `beta` must be a `SharedVariable`")
 
     @pytest.mark.xfail(reason="Depends on ModelGraph")
-    def test_model_to_graphviz_for_model_with_data_container(self):
+    def test_model_to_graphviz_for_model_with_data_container(self, tmp_path):
         with pm.Model() as model:
             x = pm.ConstantData("x", [1.0, 2.0, 3.0])
             y = pm.MutableData("y", [1.0, 2.0, 3.0])
@@ -307,6 +309,11 @@ def test_model_to_graphviz_for_model_with_data_container(self):
             for expected in expected_substrings:
                 assert expected in g.source
 
+        pm.model_to_graphviz(model, save=tmp_path / "model.png")
+        assert path.exists(tmp_path / "model.png")
+        pm.model_to_graphviz(model, save=tmp_path / "a_model", dpi=100)
+        assert path.exists(tmp_path / "a_model.png")
+
     def test_explicit_coords(self, seeded_test):
         N_rows = 5
         N_cols = 7