Consistently get version string, ignoring alpha/beta

tests/functional/test_install.py

@@ -1306,7 +1306,7 @@ def test_double_install_fail(script):
 def _get_expected_error_text():
     return (
         "Package 'pkga' requires a different Python: {} not in '<1.0'"
-    ).format(sys.version.split()[0])
+    ).format('.'.join(map(str, sys.version_info[:3])))
 
 
 def test_install_incompatible_python_requires(script):