numpy · charris · Aug 20, 2016 · Jul 20, 2016
diff --git a/numpy/__init__.py b/numpy/__init__.py
@@ -109,56 +109,8 @@
 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.
-
-    The nose tester turns ordinary Deprecation warnings into test failures.
-    That makes it hard to deprecate whole modules, because they get
-    imported by default. So this is a special Deprecation warning that the
-    nose tester will let pass without making tests fail.
-
-    """
-    pass
-
-
-class VisibleDeprecationWarning(UserWarning):
-    """Visible deprecation warning.
-
-    By default, python will not show deprecation warnings, so this class
-    can be used when a very visible warning is helpful, for example because
-    the usage is most likely a user bug.
-
-    """
-    pass
-
-
-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.
-    """
-    pass
-
-
-# oldnumeric and numarray were removed in 1.9. In case some packages import
-# but do not use them, we define them here for backward compatibility.
-oldnumeric = 'removed'
-numarray = 'removed'
-
+from ._globals import ModuleDeprecationWarning, VisibleDeprecationWarning
+from ._globals import _NoValue
 
 # We first need to detect if we're being called as part of the numpy setup
 # procedure itself in a reliable manner.
@@ -177,6 +129,7 @@ class _NoValue:
         its source directory; please exit the numpy source tree, and relaunch
         your python interpreter from there."""
         raise ImportError(msg)
+
     from .version import git_revision as __git_revision__
     from .version import version as __version__
 
@@ -239,3 +192,8 @@ def pkgload(*packages, **options):
     warnings.filterwarnings("ignore", message="numpy.dtype size changed")
     warnings.filterwarnings("ignore", message="numpy.ufunc size changed")
     warnings.filterwarnings("ignore", message="numpy.ndarray size changed")
+
+    # oldnumeric and numarray were removed in 1.9. In case some packages import
+    # but do not use them, we define them here for backward compatibility.
+    oldnumeric = 'removed'
+    numarray = 'removed'
diff --git a/numpy/_globals.py b/numpy/_globals.py
@@ -0,0 +1,62 @@
+"""
+Module defining global singleton classes.
+
+This module raises a RuntimeError if an attempt to reload it is made. In that
+way the identities of the classes defined here are fixed and will remain so
+even if numpy itself is reloaded. In particular, a function like the following
+will still work correctly after numpy is reloaded::
+
+    def foo(arg=np._NoValue):
+        if arg is np._NoValue:
+            ...
+
+That was not the case when the singleton classes were defined in the numpy
+``__init__.py`` file. See gh-7844 for a discussion of the reload problem that
+motivated this module.
+
+"""
+from __future__ import division, absolute_import, print_function
+
+
+__ALL__ = [
+    'ModuleDeprecationWarning', 'VisibleDeprecationWarning', '_NoValue'
+    ]
+
+
+# Disallow reloading this module so as to preserve the identities of the
+# classes defined here.
+if '_is_loaded' in globals():
+    raise RuntimeError('Reloading numpy._globals is not allowed')
+_is_loaded = True
+
+
+class ModuleDeprecationWarning(DeprecationWarning):
+    """Module deprecation warning.
+
+    The nose tester turns ordinary Deprecation warnings into test failures.
+    That makes it hard to deprecate whole modules, because they get
+    imported by default. So this is a special Deprecation warning that the
+    nose tester will let pass without making tests fail.
+
+    """
+    pass
+
+
+class VisibleDeprecationWarning(UserWarning):
+    """Visible deprecation warning.
+
+    By default, python will not show deprecation warnings, so this class
+    can be used when a very visible warning is helpful, for example because
+    the usage is most likely a user bug.
+
+    """
+    pass
+
+
+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.
+    """
+    pass
diff --git a/numpy/tests/test_reloading.py b/numpy/tests/test_reloading.py
@@ -2,21 +2,29 @@
 
 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():
+def test_numpy_reloading():
     # gh-7844. Also check that relevant globals retain their identity.
+    import numpy as np
+    import numpy._globals
+
     _NoValue = np._NoValue
     VisibleDeprecationWarning = np.VisibleDeprecationWarning
     ModuleDeprecationWarning = np.ModuleDeprecationWarning
 
-    assert_raises(RuntimeError, reload, np)
+    reload(np)
+    assert_(_NoValue is np._NoValue)
+    assert_(ModuleDeprecationWarning is np.ModuleDeprecationWarning)
+    assert_(VisibleDeprecationWarning is np.VisibleDeprecationWarning)
+
+    assert_raises(RuntimeError, reload, numpy._globals)
+    reload(np)
     assert_(_NoValue is np._NoValue)
     assert_(ModuleDeprecationWarning is np.ModuleDeprecationWarning)
     assert_(VisibleDeprecationWarning is np.VisibleDeprecationWarning)