Improve error message in DAGCircuit.draw for invalid filenames

qiskit/exceptions.py

@@ -73,3 +73,7 @@ def __init__(
     def __str__(self) -> str:
         """Return the message."""
         return repr(self.message)
+
+
+class InvalidFileError(QiskitError):
+    """Raised when the file provided is not valid for the specific task."""

qiskit/visualization/dag_visualization.py

@@ -21,7 +21,7 @@
 import tempfile
 
 from qiskit.dagcircuit.dagnode import DAGOpNode, DAGInNode, DAGOutNode
-from qiskit.exceptions import MissingOptionalLibraryError
+from qiskit.exceptions import MissingOptionalLibraryError, InvalidFileError
 from .exceptions import VisualizationError
 
 try:
@@ -31,6 +31,63 @@
 except ImportError:
     HAS_PIL = False
 
+FILENAME_EXTENSIONS = [
+    "bmp",
+    "canon",
+    "cgimage",
+    "cmap",
+    "cmapx",
+    "cmapx_np",
+    "dot",
+    "dot_json",
+    "eps exr",
+    "fig",
+    "gd",
+    "gd2",
+    "gif",
+    "gv",
+    "icns",
+    "ico",
+    "imap",
+    "imap_np",
+    "ismap",
+    "jp2",
+    "jpe",
+    "jpeg",
+    "jpg",
+    "json",
+    "json0",
+    "mp",
+    "pct",
+    "pdf",
+    "pic",
+    "pict",
+    "plain",
+    "plain-ext",
+    "png",
+    "pov",
+    "ps",
+    "ps2",
+    "psd",
+    "sgi",
+    "svg",
+    "svgz",
+    "tga",
+    "tif",
+    "tiff",
+    "tk",
+    "vdx",
+    "vml",
+    "vmlz",
+    "vrml",
+    "wbmp",
+    "webp",
+    "xdot",
+    "xdot1.2",
+    "xdot1.4",
+    "xdot_json",
+]
+
 
 def dag_drawer(dag, scale=0.7, filename=None, style="color"):
     """Plot the directed acyclic graph (dag) to represent operation dependencies
@@ -59,6 +116,7 @@ def dag_drawer(dag, scale=0.7, filename=None, style="color"):
     Raises:
         VisualizationError: when style is not recognized.
         MissingOptionalLibraryError: when pydot or pillow are not installed.
+        InvalidFileError: when filename provided is not valid
 
     Example:
         .. jupyter-execute::
@@ -166,7 +224,14 @@ def edge_attr_func(edge):
     dot = pydot.graph_from_dot_data(dot_str)[0]
 
     if filename:
+        if "." not in filename:
+            raise InvalidFileError("Parameter 'filename' must be in format 'name.extension'")
         extension = filename.split(".")[-1]
+        if extension not in FILENAME_EXTENSIONS:
+            raise InvalidFileError(
+                "Filename extension must be one of: "
+                + " ".join([str(elem) for elem in FILENAME_EXTENSIONS])
+            )
         dot.write(filename, format=extension)
         return None
     elif ("ipykernel" in sys.modules) and ("spyder" not in sys.modules):

test/python/visualization/test_dag_drawer.py

@@ -17,6 +17,7 @@
 from qiskit import QuantumRegister, QuantumCircuit
 from qiskit.test import QiskitTestCase
 from qiskit.tools.visualization import dag_drawer
+from qiskit.exceptions import InvalidFileError
 from qiskit.visualization.exceptions import VisualizationError
 from qiskit.converters import circuit_to_dag
 
@@ -36,6 +37,32 @@ def test_dag_drawer_invalid_style(self):
         """Test dag draw with invalid style."""
         self.assertRaises(VisualizationError, dag_drawer, self.dag, style="multicolor")
 
+    def test_dag_drawer_checks_filename_correct_format(self):
+        """filename must contain name and extension"""
+        try:
+            dag_drawer(self.dag, filename="aaabc")
+            self.fail("Expected error not raised!")
+        except InvalidFileError as exception_instance:
+            self.assertEqual(
+                exception_instance.message,
+                "Parameter 'filename' must be in format 'name.extension'",
+            )
+
+    def test_dag_drawer_checks_filename_extension(self):
+        """filename must have a valid extension"""
+        try:
+            dag_drawer(self.dag, filename="aa.abc")
+            self.fail("Expected error not raised!")
+        except InvalidFileError as exception_instance:
+            self.assertEqual(
+                exception_instance.message,
+                "Filename extension must be one of: bmp canon cgimage cmap cmapx cmapx_np "
+                "dot dot_json eps exr fig gd gd2 gif gv icns ico imap imap_np ismap jp2 "
+                "jpe jpeg jpg json json0 mp pct pdf pic pict plain plain-ext png pov "
+                "ps ps2 psd sgi svg svgz tga tif tiff tk vdx vml vmlz vrml wbmp webp "
+                "xdot xdot1.2 xdot1.4 xdot_json",
+            )
+
 
 if __name__ == "__main__":
     unittest.main(verbosity=2)