From c34203d56c6fb08a83fdd2a971de4bdd83ea7124 Mon Sep 17 00:00:00 2001
From: JSap0914 <JSap0914@users.noreply.github.com>
Date: Wed, 17 Jun 2026 16:29:03 +0900
Subject: [PATCH] fix(init): validate Python version constraint in interactive
 prompt

The interactive Python version prompt in `poetry init` accepted
arbitrary strings without validation, silently writing invalid
constraints like `invalid-python` verbatim into `pyproject.toml`.
This inconsistency existed because PR #10909 added
`_validate_version_constraint` to the dependency-version prompt but
left the Python-version prompt unguarded.

Apply the same validator (`_validate_version_constraint`) and the same
`set_max_attempts(3)` to the Compatible Python versions question.  Invalid
constraints now raise a clear error and re-prompt the user, consistent
with the dependency version and author validators in the same command.

Verification:
  pytest tests/console/commands/test_init.py \
      -k test_python_version_constraint_validated_in_interactive_prompt
---
 src/poetry/console/commands/init.py |  2 ++
 tests/console/commands/test_init.py | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/poetry/console/commands/init.py b/src/poetry/console/commands/init.py
index a0921fdd1eb..2f9cdccca8b 100644
--- a/src/poetry/console/commands/init.py
+++ b/src/poetry/console/commands/init.py
@@ -181,6 +181,8 @@ def _init_pyproject(
                     f"Compatible Python versions [<comment>{python}</comment>]: ",
                     default=python,
                 )
+                question.set_validator(self._validate_version_constraint)
+                question.set_max_attempts(3)
                 python = self.ask(question)
 
         if is_interactive:
diff --git a/tests/console/commands/test_init.py b/tests/console/commands/test_init.py
index 935f6d1d9cb..c6d5d1dc91a 100644
--- a/tests/console/commands/test_init.py
+++ b/tests/console/commands/test_init.py
@@ -1048,6 +1048,29 @@ def test_validate_version_constraint_rejects_invalid_inputs(invalid: str) -> Non
         InitCommand._validate_version_constraint(invalid)
 
 
+def test_python_version_constraint_validated_in_interactive_prompt(
+    tester: CommandTester,
+) -> None:
+    """Invalid Python version constraints should be rejected and re-prompted."""
+    inputs = [
+        "my-package",      # Package name
+        "1.2.3",           # Version
+        "",                # Description
+        "n",               # Author
+        "",                # License
+        "invalid-python",  # Python version -- INVALID, gets rejected
+        ">=3.8",           # Python version -- VALID on retry
+        "n",               # Interactive packages
+        "n",               # Interactive dev packages
+        "\n",              # Generate
+    ]
+    tester.execute(inputs="\n".join(inputs))
+    output = tester.io.fetch_output()
+
+    assert 'requires-python = ">=3.8"' in output
+    assert 'requires-python = "invalid-python"' not in output
+
+
 @pytest.mark.parametrize(
     "author",
     [