From c2728bff7a0793ee4c9957f23cd581098b469142 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@redhat.com>
Date: Thu, 21 Jun 2018 15:28:26 +0200
Subject: [PATCH 1/2] bpo-33932: Calling Py_Initialize() twice does nothing

Calling Py_Initialize() twice does nothing, instead of failing with a
fatal error: restore the Python 3.6 behaviour.
---
 Lib/test/test_embed.py                             |  9 +++++++++
 .../C API/2018-06-21-15-29-59.bpo-33932.VSlXyS.rst |  2 ++
 Programs/_testembed.c                              | 14 ++++++++++++++
 Python/pylifecycle.c                               |  3 ++-
 4 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/C API/2018-06-21-15-29-59.bpo-33932.VSlXyS.rst

diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index c52cb9948782df..f3b60433ccc131 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -229,6 +229,15 @@ def test_bpo20891(self):
         self.assertEqual(out, '')
         self.assertEqual(err, '')
 
+    def test_initialize_twice(self):
+        """
+        bpo-33932: Calling Py_Initialize() twice should do nothing (and not
+        crash!).
+        """
+        out, err = self.run_embedded_interpreter("initialize_twice")
+        self.assertEqual(out, '')
+        self.assertEqual(err, '')
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/NEWS.d/next/C API/2018-06-21-15-29-59.bpo-33932.VSlXyS.rst b/Misc/NEWS.d/next/C API/2018-06-21-15-29-59.bpo-33932.VSlXyS.rst
new file mode 100644
index 00000000000000..90ca3ece091987
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2018-06-21-15-29-59.bpo-33932.VSlXyS.rst	
@@ -0,0 +1,2 @@
+Calling Py_Initialize() twice does nothing, instead of failing with a fatal
+error: restore the Python 3.6 behaviour.
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index 7406470ae65c58..b8827f074b9cce 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -263,6 +263,19 @@ static int test_bpo20891(void)
     return 0;
 }
 
+static int test_initialize_twice(void)
+{
+    _testembed_Py_Initialize();
+
+    /* bpo-33932: Calling Py_Initialize() twice should do nothing
+     * (and not crash!). */
+    Py_Initialize();
+
+    Py_Finalize();
+
+    return 0;
+}
+
 
 /* *********************************************************
  * List of test cases and the function that implements it.
@@ -288,6 +301,7 @@ static struct TestCase TestCases[] = {
     { "pre_initialization_api", test_pre_initialization_api },
     { "pre_initialization_sys_options", test_pre_initialization_sys_options },
     { "bpo20891", test_bpo20891 },
+    { "initialize_twice", test_initialize_twice },
     { NULL, NULL }
 };
 
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 958219b744580d..8d57bda8914112 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -616,7 +616,8 @@ _Py_InitializeCore(const _PyCoreConfig *core_config)
     }
 
     if (_PyRuntime.initialized) {
-        return _Py_INIT_ERR("main interpreter already initialized");
+        /* bpo-33932: Calling Py_Initialize() twice does nothing. */
+        return _Py_INIT_OK();
     }
     if (_PyRuntime.core_initialized) {
         return _Py_INIT_ERR("runtime core already initialized");

From 66e0a374aa608789b6a8021f2859449a1b8cca2b Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@redhat.com>
Date: Thu, 21 Jun 2018 17:31:05 +0200
Subject: [PATCH 2/2] Fix _Py_InitializeEx_Private()

Exit early if Python is already initialized. Revert my previous
change in _Py_InitializeCore().
---
 Python/pylifecycle.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 8d57bda8914112..9bf0ebd35d0dc1 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -616,8 +616,7 @@ _Py_InitializeCore(const _PyCoreConfig *core_config)
     }
 
     if (_PyRuntime.initialized) {
-        /* bpo-33932: Calling Py_Initialize() twice does nothing. */
-        return _Py_INIT_OK();
+        return _Py_INIT_ERR("main interpreter already initialized");
     }
     if (_PyRuntime.core_initialized) {
         return _Py_INIT_ERR("runtime core already initialized");
@@ -893,6 +892,11 @@ _Py_InitializeMainInterpreter(const _PyMainInterpreterConfig *config)
 _PyInitError
 _Py_InitializeEx_Private(int install_sigs, int install_importlib)
 {
+    if (_PyRuntime.initialized) {
+        /* bpo-33932: Calling Py_Initialize() twice does nothing. */
+        return _Py_INIT_OK();
+    }
+
     _PyCoreConfig config = _PyCoreConfig_INIT;
     _PyInitError err;