pyversions: add support for DEBPYTHON_{DEFAULT,SUPPORTED}

debian/changelog

@@ -11,9 +11,9 @@ python-defaults (2.7.3-1) unstable; urgency=low
        + "/usr/bin/python2" → "/usr/bin/python"
     - new --shebang option to replace all shebangs in bin dirs
       (example: --shebang /usr/bin/python2.6)
-  * dh_python2, pycompile: allow to override system's list of supported
-    Python versions via DEBPYTHON_SUPPORTED and default Python version via
-    DEBPYTHON_DEFAULT env. variables
+  * pyversions, dh_python2, pycompile: allow to override system's list of
+    supported Python versions via DEBPYTHON_SUPPORTED and default Python
+    version via DEBPYTHON_DEFAULT env. variables
 
   [ Scott Kitterman ]
   * Bump upstream version to match current unstable/wheezy python2.7 version

debian/pyversions.py

@@ -110,7 +110,8 @@ def unsupported_versions(version_only=False):
     else:
         return _unsupported_versions
 
-_supported_versions = None
+_supported_versions = ["python%s" % ver for ver in \
+                       os.environ.get('DEBPYTHON_SUPPORTED', '').split()]
 def supported_versions(version_only=False):
     global _supported_versions
     if not _supported_versions:
@@ -144,7 +145,9 @@ def supported_versions(version_only=False):
     else:
         return _supported_versions
 
-_default_version = None
+_default_version = "python%s" % os.environ.get('DEBPYTHON_DEFAULT', '')
+if _default_version == 'python':
+    _default_version = None
 def default_version(version_only=False):
     global _default_version
     if not _default_version: