Add Format method to pythonexception (pythonnet#1031)

slide · web-flow · commit 5d28a8d9244e · 2020-04-08T16:50:33.000-07:00
Allows formatting a PythonException using traceback.format_exception
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -14,6 +14,7 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 -   Added support for Jetson Nano.
 -   Added support for __len__ for .NET classes that implement ICollection
 -   Added `object.GetRawPythonProxy() -> PyObject` extension method, that bypasses any conversions
+-   Added PythonException.Format method to format exceptions the same as traceback.format_exception
 
 ### Changed
 
diff --git a/src/embed_tests/TestPythonException.cs b/src/embed_tests/TestPythonException.cs
@@ -54,5 +54,41 @@ public void TestPythonErrorTypeName()
                 Assert.That(ex.PythonTypeName, Is.EqualTo("ModuleNotFoundError").Or.EqualTo("ImportError"));
             }
         }
+
+        [Test]
+        public void TestPythonExceptionFormat()
+        {
+            try
+            {
+                PythonEngine.Exec("raise ValueError('Error!')");
+                Assert.Fail("Exception should have been raised");
+            }
+            catch (PythonException ex)
+            {
+                Assert.That(ex.Format(), Does.Contain("Traceback").And.Contains("(most recent call last):").And.Contains("ValueError: Error!"));
+            }
+        }
+
+        [Test]
+        public void TestPythonExceptionFormatNoError()
+        {
+            var ex = new PythonException();
+            Assert.AreEqual(ex.StackTrace, ex.Format());
+        }
+
+        [Test]
+        public void TestPythonExceptionFormatNoTraceback()
+        {
+            try
+            {
+                var module = PythonEngine.ImportModule("really____unknown___module");
+                Assert.Fail("Unknown module should not be loaded");
+            }
+            catch (PythonException ex)
+            {
+                // ImportError/ModuleNotFoundError do not have a traceback when not running in a script 
+                Assert.AreEqual(ex.StackTrace, ex.Format());
+            }
+        }
     }
 }
diff --git a/src/runtime/pythonexception.cs b/src/runtime/pythonexception.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Runtime.CompilerServices;
+using System.Text;
 
 namespace Python.Runtime
 {
@@ -145,6 +146,47 @@ public string PythonTypeName
             get { return _pythonTypeName; }
         }
 
+        /// <summary>
+        /// Formats this PythonException object into a message as would be printed
+        /// out via the Python console. See traceback.format_exception
+        /// </summary>
+        public string Format()
+        {
+            string res;
+            IntPtr gs = PythonEngine.AcquireLock();
+            try
+            {
+                if (_pyTB != IntPtr.Zero && _pyType != IntPtr.Zero && _pyValue != IntPtr.Zero)
+                {
+                    Runtime.XIncref(_pyType);
+                    Runtime.XIncref(_pyValue);
+                    Runtime.XIncref(_pyTB);
+                    using (PyObject pyType = new PyObject(_pyType))
+                    using (PyObject pyValue = new PyObject(_pyValue))
+                    using (PyObject pyTB = new PyObject(_pyTB))
+                    using (PyObject tb_mod = PythonEngine.ImportModule("traceback"))
+                    {
+                        var buffer = new StringBuilder();
+                        var values = tb_mod.InvokeMethod("format_exception", pyType, pyValue, pyTB);
+                        foreach (PyObject val in values)
+                        {
+                            buffer.Append(val.ToString());
+                        }
+                        res = buffer.ToString();
+                    }
+                }
+                else
+                {
+                    res = StackTrace;
+                }
+            }
+            finally
+            {
+                PythonEngine.ReleaseLock(gs);
+            }
+            return res;
+        }
+
         /// <summary>
         /// Dispose Method
         /// </summary>
