#432 Use importlib.metadata.version to get the version (#502)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Adi Roiban <adi.roiban@chevah.com>
Co-authored-by: Adi Roiban <adiroiban@gmail.com>
Co-authored-by: Chris Beaven <smileychris@gmail.com>

pyproject.toml

@@ -31,6 +31,7 @@ requires-python = ">=3.8"
 dependencies = [
     "click",
     "importlib-resources>=5; python_version<'3.10'",
+    "importlib-metadata>=4.6; python_version<'3.10'",
     "incremental",
     "jinja2",
     "tomli; python_version<'3.11'",

src/towncrier/_project.py

@@ -5,17 +5,24 @@
 Responsible for getting the version and name from a project.
 """
 
-
 from __future__ import annotations
 
 import sys
 
 from importlib import import_module
+from importlib.metadata import version as metadata_version
 from types import ModuleType
+from typing import Any
 
 from incremental import Version as IncrementalVersion
 
 
+if sys.version_info >= (3, 10):
+    from importlib.metadata import packages_distributions
+else:
+    from importlib_metadata import packages_distributions  # type: ignore
+
+
 def _get_package(package_dir: str, package: str) -> ModuleType:
     try:
         module = import_module(package)
@@ -37,13 +44,40 @@ def _get_package(package_dir: str, package: str) -> ModuleType:
     return module
 
 
+def _get_metadata_version(package: str) -> str | None:
+    """
+    Try to get the version from the package metadata.
+    """
+    distributions = packages_distributions()
+    distribution_names = distributions.get(package)
+    if not distribution_names or len(distribution_names) != 1:
+        # We can only determine the version if there is exactly one matching distribution.
+        return None
+    return metadata_version(distribution_names[0])
+
+
 def get_version(package_dir: str, package: str) -> str:
+    """
+    Get the version of a package.
+
+    Try to extract the version from the distribution version metadata that matches
+    `package`, then fall back to looking for the package in `package_dir`.
+    """
+    version: Any
+
+    # First try to get the version from the package metadata.
+    if version := _get_metadata_version(package):
+        return version
+
+    # When no version if found, fall back to looking for the package in `package_dir`.
     module = _get_package(package_dir, package)
 
     version = getattr(module, "__version__", None)
 
     if not version:
-        raise Exception("No __version__, I don't know how else to look")
+        raise Exception(
+            f"No __version__ or metadata version info for the '{package}' package."
+        )
 
     if isinstance(version, str):
         return version.strip()

src/towncrier/newsfragments/432.feature.rst

@@ -0,0 +1 @@
+Inferring the version of a Python package now tries to use the metadata of the installed package before importing the package explicitly (which only looks for ``[package].__version__``).

src/towncrier/test/test_project.py

@@ -4,7 +4,8 @@
 import os
 import sys
 
-from unittest import skipIf
+from importlib.metadata import version as metadata_version
+from unittest import mock
 
 from click.testing import CliRunner
 from twisted.trial.unittest import TestCase
@@ -14,12 +15,6 @@
 from .helpers import write
 
 
-try:
-    from importlib.metadata import version as metadata_version
-except ImportError:
-    metadata_version = None
-
-
 towncrier_cli.name = "towncrier"
 
 
@@ -50,7 +45,6 @@ def test_tuple(self):
         version = get_version(temp, "mytestproja")
         self.assertEqual(version, "1.3.12")
 
-    @skipIf(metadata_version is None, "Needs importlib.metadata.")
     def test_incremental(self):
         """
         An incremental Version __version__  is picked up.
@@ -60,6 +54,14 @@ def test_incremental(self):
         with self.assertWarnsRegex(
             DeprecationWarning, "Accessing towncrier.__version__ is deprecated.*"
         ):
+            # Previously this triggered towncrier.__version__ but now the first version
+            # check is from the package metadata. Let's mock out that part to ensure we
+            # can get incremental versions from __version__ still.
+            with mock.patch(
+                "towncrier._project._get_metadata_version", return_value=None
+            ):
+                version = get_version(pkg, "towncrier")
+
             version = get_version(pkg, "towncrier")
 
         with self.assertWarnsRegex(
@@ -70,6 +72,13 @@ def test_incremental(self):
         self.assertEqual(metadata_version("towncrier"), version)
         self.assertEqual("towncrier", name)
 
+    def test_version_from_metadata(self):
+        """
+        A version from package metadata is picked up.
+        """
+        version = get_version(".", "towncrier")
+        self.assertEqual(metadata_version("towncrier"), version)
+
     def _setup_missing(self):
         """
         Create a minimalistic project with missing metadata in a temporary
@@ -91,10 +100,12 @@ def test_missing_version(self):
         tmp_dir = self._setup_missing()
 
         with self.assertRaises(Exception) as e:
+            # The 'missing' package has no __version__ string.
             get_version(tmp_dir, "missing")
 
         self.assertEqual(
-            ("No __version__, I don't know how else to look",), e.exception.args
+            ("No __version__ or metadata version info for the 'missing' package.",),
+            e.exception.args,
         )
 
     def test_missing_version_project_name(self):