Check current python version

Author: yokomotod

src/poetry/utils/env.py

@@ -453,6 +453,19 @@ def __init__(self, expected: str, given: Optional[str] = None) -> None:
         super().__init__(message)
 
 
+class InvalidCurrentPythonVersionError(EnvError):
+    def __init__(self, expected: str, given: str) -> None:
+        message = (
+            "Current Python version ({}) "
+            "is not allowed by the project ({}).\n"
+            'Please change python executable via the "env use" command.'.format(
+                given, expected
+            )
+        )
+
+        super().__init__(message)
+
+
 class EnvManager:
     """
     Environments manager
@@ -812,6 +825,13 @@ def create_venv(
 
         if env.is_venv() and not force:
             # Already inside a virtualenv.
+            current_python = Version.parse(
+                ".".join(str(c) for c in env.version_info[:3])
+            )
+            if not self._poetry.package.python_constraint.allows(current_python):
+                raise InvalidCurrentPythonVersionError(
+                    self._poetry.package.python_versions, current_python
+                )
             return env
 
         create_venv = self._poetry.config.get("virtualenvs.create")

tests/utils/test_env.py

@@ -25,6 +25,7 @@
 from poetry.utils.env import EnvCommandError
 from poetry.utils.env import EnvManager
 from poetry.utils.env import GenericEnv
+from poetry.utils.env import InvalidCurrentPythonVersionError
 from poetry.utils.env import NoCompatiblePythonVersionFound
 from poetry.utils.env import SystemEnv
 from poetry.utils.env import VirtualEnv
@@ -994,6 +995,28 @@ def test_create_venv_uses_patch_version_to_detect_compatibility_with_executable(
     )
 
 
+def test_create_venv_fails_if_current_python_version_is_not_supported(manager, poetry):
+    if "VIRTUAL_ENV" in os.environ:
+        del os.environ["VIRTUAL_ENV"]
+
+    manager.create_venv(NullIO())
+
+    version = Version.parse(".".join(str(c) for c in sys.version_info[:3]))
+    poetry.package.python_versions = "~{}".format(
+        ".".join(str(c) for c in (version.major, version.minor + 1, 0))
+    )
+
+    with pytest.raises(InvalidCurrentPythonVersionError) as e:
+        manager.create_venv(NullIO())
+
+    expected_message = (
+        "Current Python version (3.9.5) is not allowed by the project (~3.10.0).\n"
+        'Please change python executable via the "env use" command.'
+    )
+
+    assert expected_message == str(e.value)
+
+
 def test_activate_with_in_project_setting_does_not_fail_if_no_venvs_dir(
     manager: EnvManager,
     poetry: "Poetry",