Improve error message in DAGCircuit.draw for invalid filenames (#7447…

…) (#7531)

* dag_drawer should check the existence of filename extension

* fix review comments

* add release note

* Reword release note

Co-authored-by: Abby Mitchell <23662430+javabster@users.noreply.github.com>
Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
(cherry picked from commit 25e1d20)

Co-authored-by: Iulia Zidaru <iuliazidaru@users.noreply.github.com>

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 +31,64 @@
 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 +117,7 @@ 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 +225,13 @@ 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(FILENAME_EXTENSIONS)
+            )
         dot.write(filename, format=extension)
         return None
     elif ("ipykernel" in sys.modules) and ("spyder" not in sys.modules):

releasenotes/notes/dag-drawer-should-check-filename-existence-4a83418a893717f6.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    :meth:`.DAGCircuit.draw` and the associated function :func:`.dag_drawer`
+    will now show a more useful error message when the provided filename is not
+    valid.

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 +37,18 @@ 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"""
+        with self.assertRaisesRegex(
+            InvalidFileError, "Parameter 'filename' must be in format 'name.extension'"
+        ):
+            dag_drawer(self.dag, filename="aaabc")
+
+    def test_dag_drawer_checks_filename_extension(self):
+        """filename must have a valid extension"""
+        with self.assertRaisesRegex(InvalidFileError, "Filename extension must be one of: .*"):
+            dag_drawer(self.dag, filename="aa.abc")
+
 
 if __name__ == "__main__":
     unittest.main(verbosity=2)