Fix #426: call subclass when deriving from Version

tomschr · tomschr · commit 232d8e809384 · 2023-09-29T14:35:42.000+02:00
When using the replace method, an instance of the Version class
is created and not the respective subclass.
diff --git a/changelog.d/426.bugfix.rst b/changelog.d/426.bugfix.rst
@@ -0,0 +1,2 @@
+Fix :meth:`~semver.version.Version.replace` method to use the derived class
+of an instance instead of :class:`~semver.version.Version` class.
diff --git a/src/semver/version.py b/src/semver/version.py
@@ -655,8 +655,8 @@ def parse(
 
     def replace(self, **parts: Union[int, Optional[str]]) -> "Version":
         """
-        Replace one or more parts of a version and return a new
-        :class:`Version` object, but leave self untouched
+        Replace one or more parts of a version and return a new :class:`Version`
+        object, but leave self untouched.
 
         .. versionadded:: 2.9.0
            Added :func:`Version.replace`
@@ -670,7 +670,7 @@ def replace(self, **parts: Union[int, Optional[str]]) -> "Version":
         version = self.to_dict()
         version.update(parts)
         try:
-            return Version(**version)  # type: ignore
+            return type(self)(**version)  # type: ignore
         except TypeError:
             unknownkeys = set(parts) - set(self.to_dict())
             error = "replace() got %d unexpected keyword argument(s): %s" % (
diff --git a/tests/test_subclass.py b/tests/test_subclass.py
@@ -17,3 +17,37 @@ def __str__(self):
 
     v = SemVerWithVPrefix.parse("v1.2.3")
     assert str(v) == "v1.2.3"
+
+
+def test_replace_from_subclass():
+    # Issue#426
+    # Taken from the example "Creating Subclasses from Version"
+    class SemVerWithVPrefix(Version):
+        """
+        A subclass of Version which allows a "v" prefix
+        """
+
+        @classmethod
+        def parse(cls, version: str) -> "SemVerWithVPrefix":
+            """
+            Parse version string to a Version instance.
+
+            :param version: version string with "v" or "V" prefix
+            :raises ValueError: when version does not start with "v" or "V"
+            :return: a new instance
+            """
+            if not version[0] in ("v", "V"):
+                raise ValueError(
+                    f"{version!r}: not a valid semantic version tag. "
+                    "Must start with 'v' or 'V'"
+                )
+            return super().parse(version[1:], optional_minor_and_patch=True)
+
+        def __str__(self) -> str:
+            # Reconstruct the tag
+            return "v" + super().__str__()
+
+    version = SemVerWithVPrefix.parse("v1.1.0")
+    dev_version = version.replace(prerelease="dev.0")
+
+    assert str(dev_version) == "v1.1.0-dev.0"

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Fix :meth:`~semver.version.Version.replace` method to use the derived class
	`2`	+of an instance instead of :class:`~semver.version.Version` class.