BUG: Allow attaching documentation twice in add_docstring

This is technically not a bug, but some IDEs and IPython have
autoreload magic which can mean that NumPy gets reloaded a second
time. This is not safe, but when it happens ignoring that an
identical docstring is already attached fixes the issue.

2 files changed, 34 insertions, 3 deletions

diff --git a/numpy/core/src/multiarray/compiled_base.c b/numpy/core/src/multiarray/compiled_base.c
index 308e72009..5cf18049d 100644
--- a/numpy/core/src/multiarray/compiled_base.c
+++ b/numpy/core/src/multiarray/compiled_base.c
@@ -1425,7 +1425,7 @@ arr_add_docstring(PyObject *NPY_UNUSED(dummy), PyObject *args)
     #else
     char *docstr;
     #endif
-    static char *msg = "already has a docstring";
+    static char *msg = "already has a different docstring";
     PyObject *tp_dict = PyArrayDescr_Type.tp_dict;
     PyObject *myobj;
     static PyTypeObject *PyMemberDescr_TypePtr = NULL;
@@ -1482,7 +1482,7 @@ arr_add_docstring(PyObject *NPY_UNUSED(dummy), PyObject *args)
         if (!(doc)) {                                                   \
             doc = docstr;                                               \
         }                                                               \
-        else {                                                          \
+        else if (strcmp(doc, docstr) != 0) {                            \
             PyErr_Format(PyExc_RuntimeError, "%s method %s", name, msg); \
             return NULL;                                                \
         }                                                               \
@@ -1507,7 +1507,12 @@ arr_add_docstring(PyObject *NPY_UNUSED(dummy), PyObject *args)
         PyObject *doc_attr;
 
         doc_attr = PyObject_GetAttrString(obj, "__doc__");
-        if (doc_attr != NULL && doc_attr != Py_None) {
+        if (doc_attr != NULL && doc_attr != Py_None &&
+                (PyUnicode_Compare(doc_attr, str) != 0)) {
+            if (PyErr_Occurred()) {
+                /* error during PyUnicode_Compare */
+                return NULL;
+            }
             PyErr_Format(PyExc_RuntimeError, "object %s", msg);
             return NULL;
         }
diff --git a/numpy/tests/test_reloading.py b/numpy/tests/test_reloading.py
index 860832be8..61ae91b00 100644
--- a/numpy/tests/test_reloading.py
+++ b/numpy/tests/test_reloading.py
@@ -1,8 +1,12 @@
 from numpy.testing import assert_raises, assert_, assert_equal
 from numpy.compat import pickle
 
+import sys
+import subprocess
+import textwrap
 from importlib import reload
 
+
 def test_numpy_reloading():
     # gh-7844. Also check that relevant globals retain their identity.
     import numpy as np
@@ -29,3 +33,25 @@ def test_novalue():
         assert_equal(repr(np._NoValue), '<no value>')
         assert_(pickle.loads(pickle.dumps(np._NoValue,
                                           protocol=proto)) is np._NoValue)
+
+
+def test_full_reimport():
+    """At the time of writing this, it is *not* truly supported, but
+    apparently enough users rely on it, for it to be an annoying change
+    when it started failing previously.
+    """
+    # Test within a new process, to ensure that we do not mess with the
+    # global state during the test run (could lead to cryptic test failures).
+    # This is generally unsafe, especially, since we also reload the C-modules.
+    code = textwrap.dedent(r"""
+        import sys
+        import numpy as np
+
+        for k in list(sys.modules.keys()):
+            if "numpy" in k:
+                del sys.modules[k]
+
+        import numpy as np
+        """)
+    p = subprocess.run([sys.executable, '-c', code])
+    assert p.returncode == 0