Changes default logger used by blib2to3 Driver (#732)

... to stop it from spamming the log when black is used as a library in another
    python application.

When used indirectly by black the logger initiated in `driver.py` will emit
thousands of debug messages making the debug level of the root logger virtually
useless. By getting a named logger instead the verbosity of logging from this
module can easily be controlled by setting its log level.

Fixes #715

blib2to3/README

@@ -11,3 +11,6 @@ Reasons for forking:
 - better ability to debug (better reprs)
 - INDENT and DEDENT don't hold whitespace and comment prefixes
 - ability to Cythonize
+
+Change Log:
+- Changes default logger used by Driver

blib2to3/pgen2/driver.py

@@ -32,7 +32,7 @@ class Driver(object):
     def __init__(self, grammar, convert=None, logger=None):
         self.grammar = grammar
         if logger is None:
-            logger = logging.getLogger()
+            logger = logging.getLogger(__name__)
         self.logger = logger
         self.convert = convert
 
@@ -157,7 +157,7 @@ def load_grammar(gt="Grammar.txt", gp=None,
                  save=True, force=False, logger=None):
     """Load the grammar (maybe from a pickle)."""
     if logger is None:
-        logger = logging.getLogger()
+        logger = logging.getLogger(__name__)
     gp = _generate_pickle_name(gt) if gp is None else gp
     if force or not _newer(gp, gt):
         logger.info("Generating grammar tables from %s", gt)

tests/test_black.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 import asyncio
+import logging
 from concurrent.futures import ThreadPoolExecutor
 from contextlib import contextmanager, redirect_stderr
 from functools import partial, wraps
@@ -37,7 +38,6 @@
 else:
     has_blackd_deps = True
 
-
 ff = partial(black.format_file_in_place, mode=black.FileMode(), fast=True)
 fs = partial(black.format_str, mode=black.FileMode())
 THIS_FILE = Path(__file__)
@@ -1356,6 +1356,21 @@ def test_shhh_click(self) -> None:
             except RuntimeError as re:
                 self.fail(f"`patch_click()` failed, exception still raised: {re}")
 
+    def test_root_logger_not_used_directly(self) -> None:
+        def fail(*args: Any, **kwargs: Any) -> None:
+            self.fail("Record created with root logger")
+
+        with patch.multiple(
+            logging.root,
+            debug=fail,
+            info=fail,
+            warning=fail,
+            error=fail,
+            critical=fail,
+            log=fail,
+        ):
+            ff(THIS_FILE)
+
     @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
     @async_test
     async def test_blackd_request_needs_formatting(self) -> None: