bpo-33128 Fix duplicated call to importlib._install_external_importers (GH-6273)

External importers were being added in both phases of the import
system initialisation.

They're only supposed to be added in the second phase, after the
import machinery has been appropriately configured.

3 files changed, 5 insertions, 5 deletions

diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 6933b41353..336ae447a8 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -852,6 +852,9 @@ class SysModuleTest(unittest.TestCase):
         check(-1<<1000, [traceback[-1]])
         check(None, traceback)
 
+    def test_no_duplicates_in_meta_path(self):
+        self.assertEqual(len(sys.meta_path), len(set(sys.meta_path)))
+
 
 @test.support.cpython_only
 class SizeofTest(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-04-24-22-31-04.bpo-33128.g2yLuf.rst b/Misc/NEWS.d/next/Core and Builtins/2018-04-24-22-31-04.bpo-33128.g2yLuf.rst
new file mode 100644
index 0000000000..66b98cdf51
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-04-24-22-31-04.bpo-33128.g2yLuf.rst
@@ -0,0 +1,2 @@
+Fix a bug that causes PathFinder to appear twice on sys.meta_path. Patch by
+Pablo Galindo Salgado.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index a9b9470c72..958219b744 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -325,11 +325,6 @@ initimport(PyInterpreterState *interp, PyObject *sysmod)
 
     /* Install importlib as the implementation of import */
     value = PyObject_CallMethod(importlib, "_install", "OO", sysmod, impmod);
-    if (value != NULL) {
-        Py_DECREF(value);
-        value = PyObject_CallMethod(importlib,
-                                    "_install_external_importers", "");
-    }
     if (value == NULL) {
         PyErr_Print();
         return _Py_INIT_ERR("importlib install failed");