Simplify subclassing Version

Fixes: #112

ChangeLog

@@ -4,6 +4,12 @@ ChangeLog
 2.10.1 (unreleased)
 -------------------
 
+*Minor:*
+
+    * `112 <https://github.com/rbarrois/python-semanticversion/issues/112>`_:
+      Functions returning a new ``Version`` instance reuse the current class,
+      helping with subclassing.
+
 *Bugfix:*
 
     * `141 <https://github.com/rbarrois/python-semanticversion/issues/141>`_:

semantic_version/base.py

@@ -132,14 +132,14 @@ def _coerce(cls, value, allow_none=False):
 
     def next_major(self):
         if self.prerelease and self.minor == self.patch == 0:
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=0,
                 patch=0,
                 partial=self.partial,
             )
         else:
-            return Version(
+            return self.__class__(
                 major=self.major + 1,
                 minor=0,
                 patch=0,
@@ -148,14 +148,14 @@ def next_major(self):
 
     def next_minor(self):
         if self.prerelease and self.patch == 0:
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor,
                 patch=0,
                 partial=self.partial,
             )
         else:
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor + 1,
                 patch=0,
@@ -164,14 +164,14 @@ def next_minor(self):
 
     def next_patch(self):
         if self.prerelease:
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor,
                 patch=self.patch,
                 partial=self.partial,
             )
         else:
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor,
                 patch=self.patch + 1,
@@ -181,7 +181,7 @@ def next_patch(self):
     def truncate(self, level='patch'):
         """Return a new Version object, truncated up to the selected level."""
         if level == 'build':
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor,
                 patch=self.patch,
@@ -190,29 +190,29 @@ def truncate(self, level='patch'):
                 partial=self.partial,
             )
         elif level == 'prerelease':
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor,
                 patch=self.patch,
                 prerelease=self.prerelease,
                 partial=self.partial,
             )
         elif level == 'patch':
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor,
                 patch=self.patch,
                 partial=self.partial,
             )
         elif level == 'minor':
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=self.minor,
                 patch=None if self.partial else 0,
                 partial=self.partial,
             )
         elif level == 'major':
-            return Version(
+            return self.__class__(
                 major=self.major,
                 minor=None if self.partial else 0,
                 patch=None if self.partial else 0,
@@ -266,7 +266,7 @@ def coerce(cls, version_string, partial=False):
         )
 
         if match.end() == len(version_string):
-            return Version(version, partial=partial)
+            return cls(version, partial=partial)
 
         rest = version_string[match.end():]
 

tests/test_base.py

@@ -405,6 +405,15 @@ def test_truncate(self):
         self.assertEqual(v.truncate("minor"), base.Version("3.2.0"))
         self.assertEqual(v.truncate("major"), base.Version("3.0.0"))
 
+    def test_subclass(self):
+        """Custom subclasses of Version returns instances of themselves."""
+        class MyVersion(base.Version):
+            pass
+
+        v = MyVersion("3.2.1-pre")
+        subv = v.truncate()
+        self.assertEqual(type(subv), MyVersion)
+
 
 class SpecItemTestCase(unittest.TestCase):
     if sys.version_info[0] <= 2: