From 5361d6967f8fb512088f210d1bf78457c8f79400 Mon Sep 17 00:00:00 2001
From: Charles Harris <charlesr.harris@gmail.com>
Date: Wed, 20 Jul 2016 11:09:36 -0600
Subject: [PATCH] BUG: Raise RuntimeError when reloading numpy is attempted.

There seems to be little use in reloading numpy as any changed modules
that are imported into numpy would need to be reloaded first in order to
see any changes. Furthermore, reloading causes problems as global
classes defined in numpy/__init__.py change their identity. Hence we
raise a RuntimeError when an attempt to reload numpy is made.

Closes #7844.
---
 numpy/__init__.py             | 27 ++++++++++++++++++---------
 numpy/tests/test_reloading.py | 26 ++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 9 deletions(-)
 create mode 100644 numpy/tests/test_reloading.py

diff --git a/numpy/__init__.py b/numpy/__init__.py
index 0fcd5097d2d1..076f61065ff8 100644
--- a/numpy/__init__.py
+++ b/numpy/__init__.py
@@ -107,8 +107,21 @@
 from __future__ import division, absolute_import, print_function
 
 import sys
+import warnings
 
+# Disallow reloading numpy. Doing that does nothing to change previously
+# loaded modules, which would need to be reloaded separately, but it does
+# change the identity of the warnings and sentinal classes defined below
+# with dire consequences when checking for identity.
+if '_is_loaded' in globals():
+    raise RuntimeError('Reloading numpy is not supported')
+_is_loaded = True
 
+
+# Define some global warnings and the _NoValue sentinal. Defining them here
+# means that their identity will change if numpy is reloaded, hence if that is
+# to be allowed they should be moved into their own, non-reloadable module.
+# Note that these should be defined (or imported) before the other imports.
 class ModuleDeprecationWarning(DeprecationWarning):
     """Module deprecation warning.
 
@@ -135,9 +148,8 @@ class VisibleDeprecationWarning(UserWarning):
 class _NoValue:
     """Special keyword value.
 
-    This class may be used as the default value assigned to a
-    deprecated keyword in order to check if it has been given a user
-    defined value.
+    This class may be used as the default value assigned to a deprecated
+    keyword in order to check if it has been given a user defined value.
     """
     pass
 
@@ -155,11 +167,8 @@ class _NoValue:
 except NameError:
     __NUMPY_SETUP__ = False
 
-
 if __NUMPY_SETUP__:
-    import sys as _sys
-    _sys.stderr.write('Running from numpy source directory.\n')
-    del _sys
+    sys.stderr.write('Running from numpy source directory.\n')
 else:
     try:
         from numpy.__config__ import show as show_config
@@ -206,7 +215,7 @@ def pkgload(*packages, **options):
     from .compat import long
 
     # Make these accessible from numpy name-space
-    #  but not imported in from numpy import *
+    # but not imported in from numpy import *
     if sys.version_info[0] >= 3:
         from builtins import bool, int, float, complex, object, str
         unicode = str
@@ -222,8 +231,8 @@ def pkgload(*packages, **options):
     __all__.extend(lib.__all__)
     __all__.extend(['linalg', 'fft', 'random', 'ctypeslib', 'ma'])
 
+
     # Filter annoying Cython warnings that serve no good purpose.
-    import warnings
     warnings.filterwarnings("ignore", message="numpy.dtype size changed")
     warnings.filterwarnings("ignore", message="numpy.ufunc size changed")
     warnings.filterwarnings("ignore", message="numpy.ndarray size changed")
diff --git a/numpy/tests/test_reloading.py b/numpy/tests/test_reloading.py
new file mode 100644
index 000000000000..141e11f6cfb0
--- /dev/null
+++ b/numpy/tests/test_reloading.py
@@ -0,0 +1,26 @@
+from __future__ import division, absolute_import, print_function
+
+import sys
+
+import numpy as np
+from numpy.testing import assert_raises, assert_, run_module_suite
+
+if sys.version_info[:2] >= (3, 4):
+    from importlib import reload
+else:
+    from imp import reload
+
+def test_reloading_exception():
+    # gh-7844. Also check that relevant globals retain their identity.
+    _NoValue = np._NoValue
+    VisibleDeprecationWarning = np.VisibleDeprecationWarning
+    ModuleDeprecationWarning = np.ModuleDeprecationWarning
+
+    assert_raises(RuntimeError, reload, np)
+    assert_(_NoValue is np._NoValue)
+    assert_(ModuleDeprecationWarning is np.ModuleDeprecationWarning)
+    assert_(VisibleDeprecationWarning is np.VisibleDeprecationWarning)
+
+
+if __name__ == "__main__":
+    run_module_suite()