gh-117535: Change unknown filename of warnings from `sys` to `<sys>` (#118018)

Lib/test/test_warnings/__init__.py

@@ -489,7 +489,7 @@ class WarnTests(BaseTest):
 
                 warning_tests.inner("spam7", stacklevel=9999)
                 self.assertEqual(os.path.basename(w[-1].filename),
-                                    "sys")
+                                    "<sys>")
 
     def test_stacklevel_import(self):
         # Issue #24305: With stacklevel=2, module-level warnings should work.
@@ -1388,7 +1388,7 @@ a=A()
         # Issue #21925: Emitting a ResourceWarning late during the Python
         # shutdown must be logged.
 
-        expected = b"sys:1: ResourceWarning: unclosed file "
+        expected = b"<sys>:0: ResourceWarning: unclosed file "
 
         # don't import the warnings module
         # (_warnings will try to import it)

Lib/warnings.py

@@ -332,8 +332,8 @@ def warn(message, category=None, stacklevel=1, source=None,
                     raise ValueError
     except ValueError:
         globals = sys.__dict__
-        filename = "sys"
-        lineno = 1
+        filename = "<sys>"
+        lineno = 0
     else:
         globals = frame.f_globals
         filename = frame.f_code.co_filename

Misc/NEWS.d/next/Library/2024-04-18-00-35-11.gh-issue-117535.0m6SIM.rst

@@ -0,0 +1 @@
+Change the unknown filename of :mod:`warnings` from ``sys`` to ``<sys>`` to clarify that it's not a real filename.

Python/_warnings.c

@@ -894,8 +894,8 @@ setup_context(Py_ssize_t stack_level,
 
     if (f == NULL) {
         globals = interp->sysdict;
-        *filename = PyUnicode_FromString("sys");
-        *lineno = 1;
+        *filename = PyUnicode_FromString("<sys>");
+        *lineno = 0;
     }
     else {
         globals = f->f_frame->f_globals;