From a8f0ebb1834455f721282a28c43b86a8ad8e50c1 Mon Sep 17 00:00:00 2001
From: Joakim Hove <joakim.hove@gmail.com>
Date: Thu, 26 Mar 2020 12:00:59 +0100
Subject: [PATCH] Enable fine grained control of Python ON | OFF

---
 opm/parser/eclipse/Python/Python.hpp     | 35 ++++++++++++++++++++++++
 src/opm/parser/eclipse/Python/Python.cpp | 21 ++++++++++++--
 tests/parser/EmbeddedPython.cpp          | 31 +++++++++++++++++++++
 3 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/opm/parser/eclipse/Python/Python.hpp b/opm/parser/eclipse/Python/Python.hpp
index fd50ed2c2..ab488317e 100644
--- a/opm/parser/eclipse/Python/Python.hpp
+++ b/opm/parser/eclipse/Python/Python.hpp
@@ -52,10 +52,45 @@ class EclipseState;
      else
          OpmLog::Error("This version of opmcommon has been built with support for embedded Python");
 
+
+  The default constructor will enable the Python interpreter if the current
+  version of opm-common has been built support for embedded Python, by using the
+  alternative Python(Enable enable) constructor you can explicitly say if you
+  want Python support or not; if that request can not be satisfied you will get
+  std::logic_error().
+
+  Observe that the real underlying Python interpreter is essentially a singleton
+  - i.e. only a one interpreter can be active at any time. The details of the
+  interaction between build configuration, constructor arg and multiple
+  instances is as follows:
+
+
+  Build:   |  Constructor arg   |  Existing instance  | Result
+  ---------|--------------------|---------------------|-------
+  True     |  OFF               |  *                  | { }
+  True     |  ON                |  False              | { Python }
+  True     |  ON                |  True               | std::logic_error
+  True     |  COND              |  True               | { }
+  True     |  COND              |  False              | { Python }
+  False    |  OFF               |  *                  | { }
+  False    |  ON                |  *                  | std::logic_error
+  False    |  COND              |  *                  | { }
+  ---------|--------------------|---------------------|-------
+
+
 */
 
+
 class Python {
 public:
+
+    enum class Enable {
+        ON,    /* Enable the Python extensions - throw std::logic_error() if it fails. */
+        COND,  /* Try to enable Python extensions*/
+        OFF    /* Do not enable Python */
+    };
+
+    explicit Python(Enable enable);
     Python();
     bool exec(const std::string& python_code) const;
     bool exec(const std::string& python_code, const Parser& parser, Deck& deck) const;
diff --git a/src/opm/parser/eclipse/Python/Python.cpp b/src/opm/parser/eclipse/Python/Python.cpp
index 829fe27c7..eed6fecfa 100644
--- a/src/opm/parser/eclipse/Python/Python.cpp
+++ b/src/opm/parser/eclipse/Python/Python.cpp
@@ -24,8 +24,25 @@
 
 namespace Opm {
 
-Python::Python() :
-    interp(std::make_shared<PythonInterp>())
+Python::Python(Enable enable) {
+    if (enable == Enable::OFF)
+        return;
+
+#ifdef EMBEDDED_PYTHON
+    if (!Py_IsInitialized())
+        this->interp = std::make_shared<PythonInterp>();
+    else if (enable == Enable::ON)
+        throw std::logic_error("An instance of the Python interpreter is already running");
+
+    return;
+#endif
+
+    if (enable == Enable::ON)
+        throw std::logic_error("The version has been built without Python support");
+}
+
+
+Python::Python() : Python(Enable::COND)
 {
 }
 
diff --git a/tests/parser/EmbeddedPython.cpp b/tests/parser/EmbeddedPython.cpp
index abf2115bf..dcdb6cdb9 100644
--- a/tests/parser/EmbeddedPython.cpp
+++ b/tests/parser/EmbeddedPython.cpp
@@ -41,6 +41,14 @@ BOOST_AUTO_TEST_CASE(INSTANTIATE) {
     BOOST_CHECK(!python);
     BOOST_CHECK_THROW(python.exec("print('Hello world')"), std::logic_error);
     BOOST_CHECK(! Python::enabled() );
+
+
+    BOOST_CHECK_THROW( Python(Python::Enable::ON), std::logic_error );
+    Python python_cond(Python::Enable::COND);
+    BOOST_CHECK(!python_cond);
+
+    Python python_off(Python::Enable::OFF);
+    BOOST_CHECK(!python_off);
 }
 
 #else
@@ -129,6 +137,29 @@ BOOST_AUTO_TEST_CASE(PYACTION) {
 }
 
 
+BOOST_AUTO_TEST_CASE(Python_Constructor) {
+    Python python_off(Python::Enable::OFF);
+    BOOST_CHECK(!python_off);
+
+    Python python_on(Python::Enable::ON);
+    BOOST_CHECK(python_on);
+
+    // Can only have one Python interpreter active at any time
+    BOOST_CHECK_THROW(Python(Python::Enable::ON), std::logic_error);
+}
+
+BOOST_AUTO_TEST_CASE(Python_Constructor2) {
+    Python python_cond1(Python::Enable::COND);
+    BOOST_CHECK(python_cond1);
+
+    Python python_cond2(Python::Enable::COND);
+    BOOST_CHECK(!python_cond2);
+}
+
 
 #endif
 
+
+
+
+