From d461edadcb248507c89418c29af994fffd07ebc6 Mon Sep 17 00:00:00 2001
From: Tom Minka <8955276+tminka@users.noreply.github.com>
Date: Mon, 21 Dec 2020 19:50:23 +0000
Subject: [PATCH 1/3] TestPythonEngineProperties.SetPythonPath avoids
 corrupting the module search path for later tests

---
 src/embed_tests/TestPythonEngineProperties.cs | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/embed_tests/TestPythonEngineProperties.cs b/src/embed_tests/TestPythonEngineProperties.cs
index 6d2d5d6cc..94eab37d8 100644
--- a/src/embed_tests/TestPythonEngineProperties.cs
+++ b/src/embed_tests/TestPythonEngineProperties.cs
@@ -181,7 +181,22 @@ public void SetProgramName()
         public void SetPythonPath()
         {
             PythonEngine.Initialize();
-            string path = PythonEngine.PythonPath;
+
+            dynamic sys = Py.Import("sys");
+            var locals = new PyDict();
+            locals.SetItem("sys", sys);
+            var result = PythonEngine.Eval("';'.join(sys.path)", null, locals.Handle);
+            // This does not work:
+            //var result = PythonEngine.Eval("import sys\n';'.join(sys.path)");
+            string path = (string)result.AsManagedObject(typeof(string));
+
+            // path should not be set to PythonEngine.PythonPath here.
+            // PythonEngine.PythonPath gets the default module search path, not the full search path.
+            // The list sys.path is initialized with this value on interpreter startup;
+            // it can be (and usually is) modified later to change the search path for loading modules.
+            // See https://docs.python.org/3/c-api/init.html#c.Py_GetPath
+            // After PythonPath is set, then PythonEngine.PythonPath will correctly return the full search path. 
+
             PythonEngine.Shutdown();
 
             PythonEngine.PythonPath = path;

From 5a81268df70a931739fa48f3befb581ee5ad5346 Mon Sep 17 00:00:00 2001
From: Tom Minka <8955276+tminka@users.noreply.github.com>
Date: Mon, 21 Dec 2020 22:40:00 +0000
Subject: [PATCH 2/3] SetPythonPath uses System.IO.Path.PathSeparator and
 imports a module under the new path

---
 src/embed_tests/TestPythonEngineProperties.cs | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/embed_tests/TestPythonEngineProperties.cs b/src/embed_tests/TestPythonEngineProperties.cs
index 94eab37d8..cd8477c82 100644
--- a/src/embed_tests/TestPythonEngineProperties.cs
+++ b/src/embed_tests/TestPythonEngineProperties.cs
@@ -182,10 +182,22 @@ public void SetPythonPath()
         {
             PythonEngine.Initialize();
 
+            const string moduleName = "pytest";
+            bool importShouldSucceed;
+            try
+            {
+                Py.Import(moduleName);
+                importShouldSucceed = true;
+            }
+            catch
+            {
+                importShouldSucceed = false;
+            }
+
             dynamic sys = Py.Import("sys");
             var locals = new PyDict();
             locals.SetItem("sys", sys);
-            var result = PythonEngine.Eval("';'.join(sys.path)", null, locals.Handle);
+            var result = PythonEngine.Eval($"'{System.IO.Path.PathSeparator}'.join(sys.path)", null, locals.Handle);
             // This does not work:
             //var result = PythonEngine.Eval("import sys\n';'.join(sys.path)");
             string path = (string)result.AsManagedObject(typeof(string));
@@ -203,6 +215,8 @@ public void SetPythonPath()
             PythonEngine.Initialize();
 
             Assert.AreEqual(path, PythonEngine.PythonPath);
+            if (importShouldSucceed) Py.Import(moduleName);
+
             PythonEngine.Shutdown();
         }
     }

From 33e5042e6784d6314e073a9090134208521d6c42 Mon Sep 17 00:00:00 2001
From: Tom Minka <8955276+tminka@users.noreply.github.com>
Date: Tue, 22 Dec 2020 17:01:10 +0000
Subject: [PATCH 3/3] SetPythonPath computes the path string in a simpler way

---
 src/embed_tests/TestPythonEngineProperties.cs | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/src/embed_tests/TestPythonEngineProperties.cs b/src/embed_tests/TestPythonEngineProperties.cs
index cd8477c82..626e3c77f 100644
--- a/src/embed_tests/TestPythonEngineProperties.cs
+++ b/src/embed_tests/TestPythonEngineProperties.cs
@@ -194,13 +194,8 @@ public void SetPythonPath()
                 importShouldSucceed = false;
             }
 
-            dynamic sys = Py.Import("sys");
-            var locals = new PyDict();
-            locals.SetItem("sys", sys);
-            var result = PythonEngine.Eval($"'{System.IO.Path.PathSeparator}'.join(sys.path)", null, locals.Handle);
-            // This does not work:
-            //var result = PythonEngine.Eval("import sys\n';'.join(sys.path)");
-            string path = (string)result.AsManagedObject(typeof(string));
+            string[] paths = Py.Import("sys").GetAttr("path").As<string[]>();
+            string path = string.Join(System.IO.Path.PathSeparator.ToString(), paths);
 
             // path should not be set to PythonEngine.PythonPath here.
             // PythonEngine.PythonPath gets the default module search path, not the full search path.