bpo-34624: Allow regex for module passed via -W or PYTHONWARNINGS

Doc/library/warnings.rst

@@ -199,16 +199,18 @@ precedence over earlier ones).
 
 Commonly used warning filters apply to either all warnings, warnings in a
 particular category, or warnings raised by particular modules or packages.
-Some examples::
+Some examples:
+
+.. code-block:: none
 
    default                      # Show all warnings (even those ignored by default)
    ignore                       # Ignore all warnings
    error                        # Convert all warnings to errors
    error::ResourceWarning       # Treat ResourceWarning messages as errors
    default::DeprecationWarning  # Show DeprecationWarning messages
    ignore,default:::mymodule    # Only report warnings triggered by "mymodule"
-   error:::mymodule[.*]         # Convert warnings to errors in "mymodule"
-                                # and any subpackages of "mymodule"
+   error:::mymodule(\..*)?      # Convert warnings to errors in "mymodule"
+                                # and any of its submodules and subpackages
 
 
 .. _default-warning-filter:

Lib/test/test_warnings/__init__.py

@@ -1157,6 +1157,26 @@ def test_envvar_and_command_line(self):
         self.assertEqual(stdout,
             b"['ignore::DeprecationWarning', 'ignore::UnicodeWarning']")
 
+    def test_module_regex(self):
+        WARN_NOWHERE = 'True'
+        WARN_IN_MAIN = "import warnings; warnings.warn('__main__ warning');"
+        WARN_IN_SUBMOD = "import test.test_warnings.data.submodule_warning;"
+        # Check the warning is ignored by default:
+        assert_python_ok("-c", WARN_IN_MAIN, PYTHONWARNINGS="")
+        assert_python_ok("-c", WARN_IN_MAIN, PYTHONWARNINGS="ignore")
+        assert_python_ok("-c", WARN_IN_SUBMOD, PYTHONWARNINGS="")
+        assert_python_ok("-c", WARN_IN_SUBMOD, PYTHONWARNINGS="ignore")
+        # The submodule warning is still ignored because the pattern selects
+        # only to the package itself, not the submodule:
+        assert_python_ok("-c", WARN_IN_SUBMOD, PYTHONWARNINGS="error:::test")
+        # Warnings can be enabled by using wildcard regex:
+        assert_python_ok("-c", WARN_NOWHERE, PYTHONWARNINGS="error:::.*")
+        assert_python_failure("-c", WARN_IN_MAIN, PYTHONWARNINGS="error:::.*")
+        assert_python_failure("-c", WARN_IN_SUBMOD, PYTHONWARNINGS="error:::.*")
+        # Warning from submodule is raised using a more specific pattern:
+        assert_python_failure("-c", WARN_IN_SUBMOD,
+            PYTHONWARNINGS=r"error:::test.test_warnings(\..*)?")
+
     def test_conflicting_envvar_and_command_line(self):
         rc, stdout, stderr = assert_python_failure("-Werror::DeprecationWarning", "-c",
             "import sys, warnings; sys.stdout.write(str(sys.warnoptions)); "

Lib/test/test_warnings/data/submodule_warning.py

@@ -0,0 +1,3 @@
+import warnings
+
+warnings.warn('submodule warning', DeprecationWarning)

Lib/warnings.py

@@ -220,12 +220,8 @@ def _setoption(arg):
                                                  for s in parts]
     action = _getaction(action)
     category = _getcategory(category)
-    if message or module:
-        import re
-    if message:
-        message = re.escape(message)
     if module:
-        module = re.escape(module) + r'\Z'
+        module = r'\A(' + module + r')\Z'
     if lineno:
         try:
             lineno = int(lineno)

Misc/NEWS.d/next/Library/2018-09-30-19-49-37.bpo-34624.UrjcKN.rst

@@ -0,0 +1,2 @@
+When passing warning filters via ``-W`` or ``PYTHONWARNINGS``, treat the
+``module`` part as regex.