Add native support for t-strings in the stdlib logging library

Author: pR0Ps

Lib/logging/__init__.py

@@ -28,6 +28,7 @@
 from types import GenericAlias
 from string import Template
 from string import Formatter as StrFormatter
+from string.templatelib import Template as TStringTemplate, Interpolation
 
 
 __all__ = ['BASIC_FORMAT', 'BufferingFormatter', 'CRITICAL', 'DEBUG', 'ERROR',
@@ -289,11 +290,14 @@ class LogRecord(object):
 
     LogRecord instances are created every time something is logged. They
     contain all the information pertinent to the event being logged. The
-    main information passed in is in msg and args, which are combined
-    using str(msg) % args to create the message field of the record. The
-    record also includes information such as when the record was created,
-    the source line where the logging call was made, and any exception
-    information to be logged.
+    main information passed in is in msg and args. These ware combined
+    using str(msg) % args to create the message field of the record. A
+    special case here is that if the msg is a t-string, it will be
+    formatted as if it was an f-string without using the provided args.
+
+    The record also includes information such as when the record was
+    created, the source line where the logging call was made, and any
+    exception information to be logged.
     """
     def __init__(self, name, level, pathname, lineno,
                  msg, args, exc_info, func=None, sinfo=None, **kwargs):
@@ -321,6 +325,12 @@ def __init__(self, name, level, pathname, lineno,
         # formatting still seem to suggest a mapping object is required.
         # Thus, while not removing the isinstance check, it does now look
         # for collections.abc.Mapping rather than, as before, dict.
+        if isinstance(msg, TStringTemplate):
+            # Pull args out of the tstring and prepend them to any provided args
+            args = (
+                {x.expression: x.value for x in msg if isinstance(x, Interpolation)},
+                *args
+            )
         if (args and len(args) == 1 and isinstance(args[0], collections.abc.Mapping)
             and args[0]):
             args = args[0]
@@ -394,7 +404,21 @@ def getMessage(self):
 
         Return the message for this LogRecord after merging any user-supplied
         arguments with the message.
-        """
+        If the messsage is a t-string object it will be formatted in the same
+        way as an f-string without any extra user-supplied arguments.
+        """
+        if isinstance(self.msg, TStringTemplate):
+            return "".join(
+                (
+                    _str_formatter.format_field(
+                        _str_formatter.convert_field(x.value, x.conversion),
+                        x.format_spec
+                    )
+                ) if isinstance(x, Interpolation)
+                else x
+                for x in self.msg
+            )
+
         msg = str(self.msg)
         if self.args:
             msg = msg % self.args