Add PythonEngine Eval and Exec #389

yagweb · 2017-02-17T08:08:25Z

"eval" and "exec" are two of the most frequently used methods when interacting with Python. However, I found there is not "eval" provided currently, this statement var flag = (IntPtr)257; in PythonEngine.RunString method makes this method can only be used as "exec".

Two .NET functions equivalent to the Python “evel” and “exec” are implemented by wrapping the PyRun_String function just like the CPython does. PythonEngine.RunString method became internal.

All the modifications located in pythonengine.cs. All the places using PythonEngine.RunString are replaced with the new PythonEngine.Exec method.

Unit tests are given in the new file "src/embed_tests/pyrunstring.cs", They can also be used as examples. List one of them below.

Eval the python expression "sys.attr1 + a + 1" and obtain its value.

dynamic sys = Py.Import("sys");
sys.attr1 = 100;
PyDict locals = new PyDict();
locals.SetItem("sys", sys);
locals.SetItem("a", new PyInt(10));

var b = PythonEngine.Eval("sys.attr1 + a + 1", null, locals.Handle)
     .AsManagedObject(typeof(Int32));

Console.WriteLine("sys.attr1 + a + 1 = {0}", b);

CHANGELOG.md will be updated later.

vmuriart

👍 looks good. Left a couple comments in terms of design choice. I'd like to merge this after #391 to ensure no unexpected behavior from Travis.

vmuriart · 2017-02-22T07:13:03Z

src/runtime/pythonengine.cs

        /// RunString Method
        /// </summary>
        /// <remarks>
        /// Run a string containing Python code. Returns the result of
        /// executing the code string as a PyObject instance, or null if
        /// an exception was raised.
        /// </remarks>
-        public static PyObject RunString(
-            string code, IntPtr? globals = null, IntPtr? locals = null
+        internal static PyObject RunString(


Couldn't this stay as a public method? Not sure how much its being used at the moment, but I wouldn't like to pull it off the API without first deprecating it.

I just re-read your statement on the pull_request, I understand this change now. I think I would still want to deprecate it first before removing it a release or two later.

@vmuriart I agree with deprecating this method first. When this method become internal, the type of its last argument _flag can be changed from enum RunFlagType to IntPtr, and the enum RunFlagType can be removed. In the Eval and Exec methods, it can calls this RunString method using Runtime.Py_eval_input and Runtime.Py_file_input for this argument.

vmuriart · 2017-02-22T07:17:04Z

src/runtime/pythonengine.cs

+        public static PyObject Eval(string code, IntPtr? globals = null, IntPtr? locals = null)
+        {
+            PyObject result = RunString(code, globals, locals, RunFlagType.Eval);
+            return result;


Should the result be checked for exception before returning?

Not needed, RunString already does that via Py.Throw.

vmuriart · 2017-02-22T23:23:39Z

src/runtime/pythonengine.cs

+        public static void Exec(string code, IntPtr? globals = null, IntPtr? locals = null)
+        {
+            PyObject result = RunString(code, globals, locals, RunFlagType.File);
+            if (result.obj != Runtime.PyNone)


@filmor then on the flip-side, is this check here then superfluous?

@vmuriart It can be removed. RunString method will always return None when passing the last parameter Runtime.Py_file_input. So this check failed only when there is a runtime bug of CPython.

vmuriart · 2017-02-22T23:34:33Z

Just ran the tests on Travis after #391. PY27 fails with Fatal Python error: auto-releasing thread-state, but no thread-state for this thread which is unrelated to these changes. Looks good overall.

Only changes would be to keep RunString public but add a deprecation warnings instead..

One of the tests is writing to stderr in the middle of the tests not sure if we can do much on it though.

- Deprecation/Removal should be a separate issue/pr - In NUnit/XUnit, expected is the first argument, actual is second. Opposite to how Python does it

vmuriart · 2017-02-24T00:11:49Z

src/embed_tests/pyrunstring.cs

@@ -24,10 +24,10 @@ public void Dispose()
        public void TestRunSimpleString()
        {
            int aa = PythonEngine.RunSimpleString("import sys");
-            Assert.AreEqual(aa, 0);


@yagweb I think you had these backwards by mistake, its the opposite other than python. I fixed them before merge.

yagweb mentioned this pull request Feb 19, 2017

Add a class to manage the context of a interaction with Python and simplify the variable exchanging #380

Closed

vmuriart reviewed Feb 22, 2017

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Add Eval(...) and Exec(...)

ea44eef

vmuriart force-pushed the add_eval branch from b95acc3 to b43f382 Compare February 23, 2017 22:28

vmuriart changed the title ~~add eval and exec~~ Add PythonEngine Eval and Exec Feb 23, 2017

vmuriart force-pushed the add_eval branch 2 times, most recently from 2886267 to bcadc48 Compare February 23, 2017 22:43

Keep RunString Public. Fix Assert.AreEqual order

2dfff9f

- Deprecation/Removal should be a separate issue/pr - In NUnit/XUnit, expected is the first argument, actual is second. Opposite to how Python does it

vmuriart force-pushed the add_eval branch from bcadc48 to 2dfff9f Compare February 23, 2017 22:43

vmuriart merged commit 9bf4239 into pythonnet:master Feb 24, 2017

vmuriart reviewed Feb 24, 2017

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This was referenced Feb 24, 2017

Deprecate Public RunString #401

Closed

add a scope class to manage the context of interaction with Python an… #381

Merged

yagweb deleted the add_eval branch February 24, 2017 08:26

vmuriart mentioned this pull request Feb 27, 2017

in C#, PythonEngine.RunString don't work. #409

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Add PythonEngine Eval and Exec #389

Add PythonEngine Eval and Exec #389

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Add PythonEngine Eval and Exec #389

Add PythonEngine Eval and Exec #389

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