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.

1 files changed, 18 insertions, 9 deletions

diff --git a/numpy/__init__.py b/numpy/__init__.py
index b05157c4a..4be750c19 100644
--- a/numpy/__init__.py
+++ b/numpy/__init__.py
@@ -107,8 +107,21 @@ Exceptions to this rule are documented.
 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 @@ try:
 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
@@ -209,7 +218,7 @@ else:
     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
@@ -225,8 +234,8 @@ else:
     __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")