bpo-31975 (PEP 565): Show DeprecationWarning in __main__ (GH-4458)

- primary change is to add a new default filter entry for
  'default::DeprecationWarning:__main__'
- secondary change is an internal one to cope with plain
  strings in the warning module's internal filter list
  (this avoids the need to create a compiled regex object
  early on during interpreter startup)
- assorted documentation updates, including many more
  examples of configuring the warnings settings
- additional tests to ensure that both the pure Python and
  the C accelerated warnings modules have the expected
  default configuration

1 files changed, 2 insertions, 0 deletions

diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
index 54ea377..a6b6634 100644
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -558,6 +558,7 @@ class CmdLineTest(unittest.TestCase):
             expected_filters = "default::Warning"
         else:
             expected_filters = ("default::Warning "
+                                "default::DeprecationWarning "
                                 "ignore::DeprecationWarning "
                                 "ignore::PendingDeprecationWarning "
                                 "ignore::ImportWarning "
@@ -626,6 +627,7 @@ class CmdLineTest(unittest.TestCase):
                             "always::UserWarning")
         if not Py_DEBUG:
             expected_filters += (" "
+                                 "default::DeprecationWarning "
                                  "ignore::DeprecationWarning "
                                  "ignore::PendingDeprecationWarning "
                                  "ignore::ImportWarning "