Lazy pydot import

pytensor/d3viz/formatting.py

@@ -12,13 +12,7 @@ import pytensor
 from pytensor.compile import Function, builders
 from pytensor.graph.basic import Apply, Constant, Variable, graph_inputs
 from pytensor.graph.fg import FunctionGraph
-from pytensor.printing import pydot_imported, pydot_imported_msg
-
-
-try:
-    from pytensor.printing import pd
-except ImportError:
-    pass
+from pytensor.printing import _try_pydot_import
 
 
 class PyDotFormatter:
@@ -41,8 +35,7 @@ class PyDotFormatter:
 
     def __init__(self, compact=True):
         """Construct PyDotFormatter object."""
-        if not pydot_imported:
-            raise ImportError("Failed to import pydot. " + pydot_imported_msg)
+        _try_pydot_import()
 
         self.compact = compact
         self.node_colors = {
@@ -115,6 +108,8 @@ class PyDotFormatter:
         pydot.Dot
             Pydot graph of `fct`
         """
+        pd = _try_pydot_import()
+
         if graph is None:
             graph = pd.Dot()
 
@@ -356,6 +351,8 @@ def type_to_str(t):
 
 def dict_to_pdnode(d):
     """Create pydot node from dict."""
+    pd = _try_pydot_import()
+
     e = dict()
     for k, v in d.items():
         if v is not None:

pytensor/printing.py

@@ -26,39 +26,6 @@ from pytensor.graph.utils import Scratchpad
 
 IDTypesType = Literal["id", "int", "CHAR", "auto", ""]
 
-pydot_imported = False
-pydot_imported_msg = ""
-try:
-    # pydot-ng is a fork of pydot that is better maintained
-    import pydot_ng as pd
-
-    if pd.find_graphviz():
-        pydot_imported = True
-    else:
-        pydot_imported_msg = "pydot-ng can't find graphviz. Install graphviz."
-except ImportError:
-    try:
-        # fall back on pydot if necessary
-        import pydot as pd
-
-        if hasattr(pd, "find_graphviz"):
-            if pd.find_graphviz():
-                pydot_imported = True
-            else:
-                pydot_imported_msg = "pydot can't find graphviz"
-        else:
-            pd.Dot.create(pd.Dot())
-            pydot_imported = True
-    except ImportError:
-        # tests should not fail on optional dependency
-        pydot_imported_msg = (
-            "Install the python package pydot or pydot-ng. Install graphviz."
-        )
-    except Exception as e:
-        pydot_imported_msg = "An error happened while importing/trying pydot: "
-        pydot_imported_msg += str(e.args)
-
-
 _logger = logging.getLogger("pytensor.printing")
 VALID_ASSOC = {"left", "right", "either"}
 
@@ -1196,6 +1163,48 @@ default_colorCodes = {
 }
 
 
+def _try_pydot_import():
+    pydot_imported = False
+    pydot_imported_msg = ""
+    try:
+        # pydot-ng is a fork of pydot that is better maintained
+        import pydot_ng as pd
+
+        if pd.find_graphviz():
+            pydot_imported = True
+        else:
+            pydot_imported_msg = "pydot-ng can't find graphviz. Install graphviz."
+    except ImportError:
+        try:
+            # fall back on pydot if necessary
+            import pydot as pd
+
+            if hasattr(pd, "find_graphviz"):
+                if pd.find_graphviz():
+                    pydot_imported = True
+                else:
+                    pydot_imported_msg = "pydot can't find graphviz"
+            else:
+                pd.Dot.create(pd.Dot())
+                pydot_imported = True
+        except ImportError:
+            # tests should not fail on optional dependency
+            pydot_imported_msg = (
+                "Install the python package pydot or pydot-ng. Install graphviz."
+            )
+        except Exception as e:
+            pydot_imported_msg = "An error happened while importing/trying pydot: "
+            pydot_imported_msg += str(e.args)
+
+    if not pydot_imported:
+        raise ImportError(
+            "Failed to import pydot. You must install graphviz "
+            "and either pydot or pydot-ng for "
+            f"`pydotprint` to work:\n {pydot_imported_msg}",
+        )
+    return pd
+
+
 def pydotprint(
     fct,
     outfile: Path | str | None = None,
@@ -1288,6 +1297,8 @@ def pydotprint(
         scan separately after the top level debugprint output.
 
     """
+    pd = _try_pydot_import()
+
     from pytensor.scan.op import Scan
 
     if colorCodes is None:
@@ -1320,12 +1331,6 @@ def pydotprint(
         outputs = fct.outputs
         topo = fct.toposort()
         fgraph = fct
-    if not pydot_imported:
-        raise RuntimeError(
-            "Failed to import pydot. You must install graphviz "
-            "and either pydot or pydot-ng for "
-            f"`pydotprint` to work:\n {pydot_imported_msg}",
-        )
 
     g = pd.Dot()
 

tests/d3viz/test_d3viz.py

@@ -9,12 +9,14 @@ import pytensor.d3viz as d3v
 from pytensor import compile
 from pytensor.compile.function import function
 from pytensor.configdefaults import config
-from pytensor.printing import pydot_imported, pydot_imported_msg
+from pytensor.printing import _try_pydot_import
 from tests.d3viz import models
 
 
-if not pydot_imported:
-    pytest.skip("pydot not available: " + pydot_imported_msg, allow_module_level=True)
+try:
+    _try_pydot_import()
+except Exception as e:
+    pytest.skip(f"pydot not available: {e!s}", allow_module_level=True)
 
 
 class TestD3Viz:

tests/d3viz/test_formatting.py

@@ -3,11 +3,13 @@ import pytest
 
 from pytensor import config, function
 from pytensor.d3viz.formatting import PyDotFormatter
-from pytensor.printing import pydot_imported, pydot_imported_msg
+from pytensor.printing import _try_pydot_import
 
 
-if not pydot_imported:
-    pytest.skip("pydot not available: " + pydot_imported_msg, allow_module_level=True)
+try:
+    _try_pydot_import()
+except Exception as e:
+    pytest.skip(f"pydot not available: {e!s}", allow_module_level=True)
 
 from tests.d3viz import models
 

tests/scan/test_printing.py

@@ -5,7 +5,7 @@ import pytensor
 import pytensor.tensor as pt
 from pytensor.configdefaults import config
 from pytensor.graph.fg import FunctionGraph
-from pytensor.printing import debugprint, pydot_imported, pydotprint
+from pytensor.printing import _try_pydot_import, debugprint, pydotprint
 from pytensor.tensor.type import dvector, iscalar, scalar, vector
 
 
@@ -686,6 +686,13 @@ def test_debugprint_compiled_fn():
         assert truth.strip() == out.strip()
 
 
+try:
+    _try_pydot_import()
+    pydot_imported = True
+except Exception:
+    pydot_imported = False
+
+
 @pytest.mark.skipif(not pydot_imported, reason="pydot not available")
 def test_pydotprint():
     def f_pow2(x_tm1):

tests/test_printing.py

@@ -17,13 +17,13 @@ from pytensor.printing import (
     PatternPrinter,
     PPrinter,
     Print,
+    _try_pydot_import,
     char_from_number,
     debugprint,
     default_printer,
     get_node_by_id,
     min_informative_str,
     pp,
-    pydot_imported,
     pydotprint,
 )
 from pytensor.tensor import as_tensor_variable
@@ -31,6 +31,13 @@ from pytensor.tensor.type import dmatrix, dvector, matrix
 from tests.graph.utils import MyInnerGraphOp, MyOp, MyVariable
 
 
+try:
+    _try_pydot_import()
+    pydot_imported = True
+except Exception:
+    pydot_imported = False
+
+
 @pytest.mark.parametrize(
     "number,s",
     [