Use the same technique in pkg_resources, relying on an 'extern' module to resolve the conditional import.

--HG--
branch : feature/issue-229

2 files changed, 45 insertions, 0 deletions

diff --git a/pkg_resources/extern/__init__.py b/pkg_resources/extern/__init__.py
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/pkg_resources/extern/__init__.py
diff --git a/pkg_resources/extern/packaging.py b/pkg_resources/extern/packaging.py
new file mode 100644
index 00000000..47f58eab
--- /dev/null
+++ b/pkg_resources/extern/packaging.py
@@ -0,0 +1,45 @@
+"""
+Handle loading a package from system or from the bundled copy
+"""
+
+import imp
+
+
+_SEARCH_PATH = ['pkg_resources._vendor.packaging', 'packaging']
+
+
+def _find_module(name, path=None):
+    """
+    Alternative to `imp.find_module` that can also search in subpackages.
+    """
+
+    parts = name.split('.')
+
+    for part in parts:
+        if path is not None:
+            path = [path]
+
+        fh, path, descr = imp.find_module(part, path)
+
+    return fh, path, descr
+
+
+def _import_in_place(search_path=_SEARCH_PATH):
+    for mod_name in search_path:
+        try:
+            mod_info = _find_module(mod_name)
+        except ImportError:
+            continue
+
+        imp.load_module(__name__, *mod_info)
+        break
+
+    else:
+        raise ImportError(
+            "The '{name}' package is required; "
+            "normally this is bundled with this package so if you get "
+            "this warning, consult the packager of your "
+            "distribution.".format(name=_SEARCH_PATH[-1]))
+
+
+_import_in_place()