Make semantic_version.py usable outside of GAE

app/models/semantic_version.py

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 import re
 from functools import total_ordering
 
-from google.appengine.ext import db
-
 @total_ordering
 class SemanticVersion(object):
     """A semantic version number. See http://semver.org/."""
 
     _RE = re.compile(r"""
       ^
       (\d+)\.(\d+)\.(\d+)                  # Version number.
       (?:-([0-9a-z-]+(?:\.[0-9a-z-]+)*))?  # Pre-release.
       (?:\+([0-9a-z-]+(?:\.[0-9a-z-]+)*))? # Build.
       $                                    # Consume entire string.
       """, re.VERBOSE | re.IGNORECASE)
 
     def __init__(self, version):
         """Parse a semantic version string."""
 
         match = SemanticVersion._RE.match(version)
-        if not match: raise db.BadValueError(
-            '"%s" is not a valid semantic version.' % version)
+        if not match:
+            raise ValueError('"%s" is not a valid semantic version.' % version)
 
         self.major = int(match.group(1))
         self.minor = int(match.group(2))
         self.patch = int(match.group(3))
         self.prerelease = _split(match.group(4))
         self.build = _split(match.group(5))
         self._text = version
 
     @property
     def is_prerelease(self):
@@ skipping 82 matching lines @@
 
     Specifically, splits the string on periods, then converts every section that
     contains only numeric digits to an integer.
     """
 
     if string is None: return
     def maybe_make_int(substring):
         if re.search(r'[^0-9]', substring): return substring
         return int(substring)
     return map(maybe_make_int, string.split('.'))