Merge pull request #147 from embray/issue-147

auto-upgrade can break when a previous install of a different package *also* auto-upgraded astropy-helpers

CHANGES.rst

@@ -17,6 +17,10 @@ astropy-helpers Changelog
 - Various fixes enabling the astropy-helpers Sphinx build command and
   Sphinx extensions to work with Sphinx 1.3. [#148]
 
+- More improvement to the ability to handle multiple versions of
+  astropy-helpers being imported in the same Python interpreter session
+  in the (somewhat rare) case of nested installs. [#147]
+
 
 1.0.1 (2015-03-04)
 ------------------

ah_bootstrap.py

@@ -282,6 +282,19 @@ def run(self):
         strategies = ['local_directory', 'local_file', 'index']
         dist = None
 
+        # First, remove any previously imported versions of astropy_helpers;
+        # this is necessary for nested installs where one package's installer
+        # is installing another package via setuptools.sandbox.run_setup, as in
+        # the case of setup_requires
+        for key in list(sys.modules):
+            try:
+                if key == PACKAGE_NAME or key.startswith(PACKAGE_NAME + '.'):
+                    del sys.modules[key]
+            except AttributeError:
+                # Sometimes mysterious non-string things can turn up in
+                # sys.modules
+                continue
+
         # Check to see if the path is a submodule
         self.is_submodule = self._check_submodule()
 
@@ -311,19 +324,6 @@ def run(self):
         # Note: Adding the dist to the global working set also activates it
         # (makes it importable on sys.path) by default.
 
-        # But first, remove any previously imported versions of
-        # astropy_helpers; this is necessary for nested installs where one
-        # package's installer is installing another package via
-        # setuptools.sandbox.run_set, as in the case of setup_requires
-        for key in list(sys.modules):
-            try:
-                if key == PACKAGE_NAME or key.startswith(PACKAGE_NAME + '.'):
-                    del sys.modules[key]
-            except AttributeError:
-                # Sometimes mysterious non-string things can turn up in
-                # sys.modules
-                continue
-
         try:
             pkg_resources.working_set.add(dist, replace=True)
         except TypeError: