lint for noarch python withotu a bound on python version

conda_smithy/lint_recipe.py

@@ -515,6 +515,18 @@ def lintify(meta, recipe_dir=None, conda_forge=False):
                 " form. See lines %s." % (bad_lines,)
             )
 
+    # 25: require a lower bound on python version
+    if build_section.get("noarch") == "python" and not outputs_section:
+        for req in run_reqs:
+            if req.startswith("python") and req != "python":
+                break
+        else:
+            lints.append(
+                "noarch: python recipes are recommended to have a lower bound "
+                "on minimum python bound. This recommendation will become "
+                "requirement in a future version."
+            )
+
     # hints
     # 1: suggest pip
     if "script" in build_section:

tests/test_lint_recipe.py

@@ -580,6 +580,33 @@ def test_bad_requirements_order(self):
         lints, hints = linter.lintify(meta)
         self.assertNotIn(expected_message, lints)
 
+    def test_noarch_python_bound(self):
+        expected_message = (
+            "noarch: python recipes are recommended to have a lower bound "
+            "on minimum python bound. This recommendation will become "
+            "requirement in a future version."
+        )
+        meta = {
+            "build": {"noarch": "python"},
+            "requirements": {"host": ["python",], "run": ["python",]},
+        }
+        lints, hints = linter.lintify(meta)
+        self.assertIn(expected_message, lints)
+
+        meta = {
+            "build": {"noarch": "python"},
+            "requirements": {"host": ["python",], "run": ["python >=2.7",]},
+        }
+        lints, hints = linter.lintify(meta)
+        self.assertNotIn(expected_message, lints)
+
+        meta = {
+            "build": {"noarch": "generic"},
+            "requirements": {"host": ["python",], "run": ["python",]},
+        }
+        lints, hints = linter.lintify(meta)
+        self.assertNotIn(expected_message, lints)
+
     def test_no_sha_with_dl(self):
         expected_message = (
             "When defining a source/url please add a sha256, "