Added python "with" construction

pythonnet · den-run-ai · May 24, 2017 · May 6, 2017 · May 6, 2017 · May 6, 2017
commit 73c40fc6d484acaed68514955963a5512d086739
diff --git a/src/embed_tests/TestPyWith.cs b/src/embed_tests/TestPyWith.cs
@@ -0,0 +1,88 @@
+using System;
+using NUnit.Framework;
+using Python.Runtime;
+
+namespace Python.EmbeddingTest
+{
+    public class TestPyWith
+    {
+        [OneTimeSetUp]
+        public void SetUp()
+        {
+            PythonEngine.Initialize();
+        }
+
+        [OneTimeTearDown]
+        public void Dispose()
+        {
+            PythonEngine.Shutdown();
+        }
+
+        /// <summary>
+        /// Test that exception is raised in context manager that ignores it.
+        /// </summary>
+        [Test]
+        public void TestPositiveWith()
+        {
+            var locals = new PyDict();
+
+            PythonEngine.Exec(@"
+class cmTest:
+    def __enter__(self):
+        print('Enter')
+        return self
+    def __exit__(self, t, v, tb):
+        # Exception not handled, return will be False
+        print('Exit')
+    def fail(self):
+        return 5 / 0
+
+a = cmTest()
+", null, locals.Handle);
+
+            var a = locals.GetItem("a");
+
+            try
+            {
+                Py.With(a, cmTest =>
+                {
+                    cmTest.fail();
+                });
+            }
+            catch (PythonException e)
+            {
+                Assert.IsTrue(e.Message.Contains("division by zero"));
+            }
+        }
+
+
+        /// <summary>
+        /// Test that exception is not raised in context manager that handles it
+        /// </summary>
+        [Test]
+        public void TestNegativeWith()
+        {
+            var locals = new PyDict();
+
+            PythonEngine.Exec(@"
+class cmTest:
+    def __enter__(self):
+        print('Enter')
+        return self
+    def __exit__(self, t, v, tb):
+        # Signal exception is handled by returning true
+        return True
+    def fail(self):
+        return 5 / 0
+
+a = cmTest()
+", null, locals.Handle);
+
+            var a = locals.GetItem("a");
+            Py.With(a, cmTest =>
+            {
+                cmTest.fail();
+            });
+        }
+    }
+}
diff --git a/src/runtime/pythonengine.cs b/src/runtime/pythonengine.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -632,5 +632,34 @@ public static void SetArgv(IEnumerable<string> argv)
                 Runtime.CheckExceptionOccurred();
             }
         }
+
+        public static void With(PyObject obj, Action<dynamic> Body)
+        {
+            // Behavior described here: 
+            // https://docs.python.org/2/reference/datamodel.html#with-statement-context-managers
+
+            IntPtr type = Runtime.PyNone;
+            IntPtr val = Runtime.PyNone;
+            IntPtr traceBack = Runtime.PyNone;
+            PythonException ex = null;
+
+            try
+            {
+                PyObject enterResult = obj.InvokeMethod("__enter__");
+
+                Body(enterResult);
+            }
+            catch (PythonException e)
+            {
+                ex = e;
+                type = ex.PyType;
+                val = ex.PyValue;
+                traceBack = ex.PyTB;
+            }
+
+            var exitResult = obj.InvokeMethod("__exit__", new PyObject(type), new PyObject(val), new PyObject(traceBack));
+
+            if (ex != null && !exitResult.IsTrue()) throw ex;
+        }
     }
 }