Closes #20242: Merged fix from 3.3.

Lib/logging/__init__.py

@@ -390,10 +390,12 @@ class StringTemplateStyle(PercentStyle):
     def format(self, record):
         return self._tpl.substitute(**record.__dict__)
 
+BASIC_FORMAT = "%(levelname)s:%(name)s:%(message)s"
+
 _STYLES = {
-    '%': PercentStyle,
+    '%': (PercentStyle, BASIC_FORMAT),
-    '{': StrFormatStyle,
+    '{': (StrFormatStyle, '{levelname}:{name}:{message}'),
-    '$': StringTemplateStyle
+    '$': (StringTemplateStyle, '${levelname}:${name}:${message}'),
 }
 
 class Formatter(object):
@@ -458,7 +460,7 @@ class Formatter(object):
         if style not in _STYLES:
             raise ValueError('Style must be one of: %s' % ','.join(
                              _STYLES.keys()))
-        self._style = _STYLES[style](fmt)
+        self._style = _STYLES[style][0](fmt)
         self._fmt = self._style._fmt
         self.datefmt = datefmt
 
@@ -1643,8 +1645,6 @@ Logger.manager = Manager(Logger.root)
 # Configuration classes and functions
 #---------------------------------------------------------------------------
 
-BASIC_FORMAT = "%(levelname)s:%(name)s:%(message)s"
-
 def basicConfig(**kwargs):
     """
     Do basic configuration for the logging system.
@@ -1718,9 +1718,12 @@ def basicConfig(**kwargs):
                     stream = kwargs.get("stream")
                     h = StreamHandler(stream)
                 handlers = [h]
-            fs = kwargs.get("format", BASIC_FORMAT)
             dfs = kwargs.get("datefmt", None)
             style = kwargs.get("style", '%')
+            if style not in _STYLES:
+                raise ValueError('Style must be one of: %s' % ','.join(
+                                 _STYLES.keys()))
+            fs = kwargs.get("format", _STYLES[style][1])
             fmt = Formatter(fs, dfs, style)
             for h in handlers:
                 if h.formatter is None:

Lib/test/test_logging.py

@@ -3517,6 +3517,22 @@ class BasicConfigTest(unittest.TestCase):
         # level is not explicitly set
         self.assertEqual(logging.root.level, self.original_logging_level)
 
+    def test_strformatstyle(self):
+        with captured_stdout() as output:
+            logging.basicConfig(stream=sys.stdout, style="{")
+            logging.error("Log an error")
+            sys.stdout.seek(0)
+            self.assertEqual(output.getvalue().strip(),
+                "ERROR:root:Log an error")
+
+    def test_stringtemplatestyle(self):
+        with captured_stdout() as output:
+            logging.basicConfig(stream=sys.stdout, style="$")
+            logging.error("Log an error")
+            sys.stdout.seek(0)
+            self.assertEqual(output.getvalue().strip(),
+                "ERROR:root:Log an error")
+
     def test_filename(self):
 
         def cleanup(h1, h2, fn):

Misc/NEWS

@@ -25,6 +25,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #20242: Fixed basicConfig() format strings for the alternative
+  formatting styles. Thanks to kespindler for the bug report and patch.
+
 - Issues #20206 and #5803: Fix edge case in email.quoprimime.encode where it
   truncated lines ending in a character needing encoding but no newline by
   using a more efficient algorithm that doesn't have the bug.