better versioning again

versioning.py

@@ -118,13 +118,8 @@ def import_file(name, path):
     return module
 
 
-def get_version():
-    """ Fallback & Test version function.
-
-        >>> get_version()
-        'no_version'
-    """
-    return 'no_version'
+# this will be overriden later
+def get_version(): return 'no_version'
 
 
 def setup_versioning():
@@ -299,12 +294,27 @@ class cmd_version_bump(Command):
             #f_out.write(f_in.read())
 
 
+# we override different commands for both environments
+_sdist = _build_py = _upload = object
 
-if "setuptools" in sys.modules:
-    from setuptools.command.build_py import build_py as _build_py
-else:
-    from distutils.command.build_py import build_py as _build_py
+def import_commands_to_override(oldschool=False):
+    """ Import the command classes to override either
+        from setuptools or distutils.
 
+        >>> import_commands_to_override()
+        >>> import_commands_to_override(True)
+    """
+    global _sdist, _build_py, _upload
+    from distutils.command.upload import upload as _upload
+
+    if not oldschool and "setuptools" in sys.modules:
+        from setuptools.command.sdist import sdist as _sdist
+        from setuptools.command.build_py import build_py as _build_py
+    else:
+        from distutils.command.sdist import sdist as _sdist
+        from distutils.command.build_py import build_py as _build_py
+
+import_commands_to_override()
 
 class cmd_build_py(_build_py):
     """ It seems as if build_py is executed when the distributed package is installed. """
@@ -344,11 +354,6 @@ class cmd_build_py(_build_py):
     #cmds["build_exe"] = cmd_build_exe
     #del cmds["build_py"]
 
-# we override different "sdist" commands for both environments
-if "setuptools" in sys.modules:
-    from setuptools.command.sdist import sdist as _sdist
-else:
-    from distutils.command.sdist import sdist as _sdist
 
 def add_to_sdist(self=None, base_dir=os.curdir, files=()):
     """ The custom part of the sdist command.
@@ -381,7 +386,7 @@ def add_to_sdist(self=None, base_dir=os.curdir, files=()):
     self_target = join(base_dir, basename(__file__))
     print("== Updating: %s" % self_target)
     try:
-        os.link(__file__, self_target)
+        os.path.exists(self_target) or os.link(__file__, self_target)
     except OSError:
         print("=== Could not add %s to sdist!" % basename(__file__))
 
@@ -399,8 +404,6 @@ class cmd_sdist(_sdist):
     make_release_tree = add_to_sdist
 
 
-from distutils.command.upload import upload as _upload
-
 def protected_upload(self=None):
     """ Allow only uploads with Python 3.
         I experienced problems earlier, when i uploaded packages built