Don't eagerly import namespace packages. This was the big reason for

branching to 0.7 now, as I wanted this wart gone before anything went
into Python 2.5.  But it's gone now, yay!

--HG--
extra : source : f3c5c19842064dd4a497baef0171aac54464a484
extra : amend_source : 3f79e71eedfc5f37a1813967bb53cf9d92a11919

4 files changed, 31 insertions, 13 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index 4214aca5..8200b99a 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -3,6 +3,19 @@ CHANGES
 =======
 
 ---
+3.0
+---
+
+* Issue #12: Namespace packages are now imported lazily.  That is, the mere
+  declaration of a namespace package in an egg on ``sys.path`` no longer
+  causes it to be imported when ``pkg_resources`` is imported.  Note that this
+  change means that all of a namespace package's ``__init__.py`` files must
+  include a ``declare_namespace()`` call in order to ensure that they will be
+  handled properly at runtime.  In 2.x it was possible to get away without
+  including the declaration, but only at the cost of forcing namespace
+  packages to be imported early, which 3.0 no longer does.
+
+---
 2.3
 ---
 
diff --git a/docs/pkg_resources.txt b/docs/pkg_resources.txt
index 8dd3e9ab..18b68db7 100644
--- a/docs/pkg_resources.txt
+++ b/docs/pkg_resources.txt
@@ -137,13 +137,16 @@ Namespace Package Support
 
 A namespace package is a package that only contains other packages and modules,
 with no direct contents of its own.  Such packages can be split across
-multiple, separately-packaged distributions.  Normally, you do not need to use
-the namespace package APIs directly; instead you should supply the
-``namespace_packages`` argument to ``setup()`` in your project's ``setup.py``.
-See the `setuptools documentation on namespace packages`_ for more information.
-
-However, if for some reason you need to manipulate namespace packages or
-directly alter ``sys.path`` at runtime, you may find these APIs useful:
+multiple, separately-packaged distributions.  They are normally used to split
+up large packages produced by a single organization, such as in the ``zope``
+namespace package for Zope Corporation packages, and the ``peak`` namespace
+package for the Python Enterprise Application Kit.
+
+To create a namespace package, you list it in the ``namespace_packages``
+argument to ``setup()``, in your project's ``setup.py``.  (See the `setuptools
+documentation on namespace packages`_ for more information on this.)  Also,
+you must add a ``declare_namespace()`` call in the package's ``__init__.py``
+file(s):
 
 ``declare_namespace(name)``
     Declare that the dotted package name `name` is a "namespace package" whose
diff --git a/pkg_resources.py b/pkg_resources.py
index 2a47c58b..2d656f1a 100644
--- a/pkg_resources.py
+++ b/pkg_resources.py
@@ -2311,7 +2311,9 @@ class Distribution(object):
         self.insert_on(path)
         if path is sys.path:
             fixup_namespace_packages(self.location)
-            list(map(declare_namespace, self._get_metadata('namespace_packages.txt')))
+            for pkg in self._get_metadata('namespace_packages.txt'):
+                if pkg in sys.modules:
+                    declare_namespace(pkg)
 
     def egg_name(self):
         """Return what this distribution's standard .egg filename should be"""
diff --git a/setuptools/command/build_py.py b/setuptools/command/build_py.py
index 090b44d2..1efabc02 100644
--- a/setuptools/command/build_py.py
+++ b/setuptools/command/build_py.py
@@ -167,12 +167,12 @@ class build_py(_build_py, Mixin2to3):
 
         f = open(init_py,'rbU')
         if 'declare_namespace'.encode() not in f.read():
-            from distutils import log
-            log.warn(
-                "WARNING: %s is a namespace package, but its __init__.py does\n"
-                "not declare_namespace(); setuptools 0.7 will REQUIRE this!\n"
+            from distutils.errors import DistutilsError
+            raise DistutilsError(
+                "Namespace package problem: %s is a namespace package, but its\n"
+                "__init__.py does not call declare_namespace()! Please fix it.\n"
                 '(See the setuptools manual under "Namespace Packages" for '
-                "details.)\n", package
+                "details.)\n" % (package,)
             )
         f.close()
         return init_py