logging: inherit output stream from existing handler

When using the logging redirection, logs will currently always be printed
to stdout, while the logging module default is to print to stderr.

Fix this by trying to inherit the stream from the existing handler, like
the code already does for the formatter.

Consider the following example:

    import logging
    import time

    from tqdm.contrib.logging import tqdm_logging_redirect

    log = logging.getLogger()
    log.warning("start")

    with tqdm_logging_redirect(range(int(4))) as pbar:
        for i in pbar:
            time.sleep(0.1)
            log.warning(f"Step {i}")

    log.warning("done")

Running this while redirecting stdout (`$ python3 log.py > /dev/null`)
without this patch will print:

    $ venv/bin/python log.py > /dev/null
    start
    100%|████████████████████████████████████████████| 4/4 [00:00<00:00,  9.87it/s]
    done

After this patch:

    $ venv/bin/python log.py > /dev/null
    start
    Step 0
    Step 1
    Step 2
    Step 3
    100%|████████████████████████████████████████████| 4/4 [00:00<00:00,  9.83it/s]
    done

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>

tests/tests_contrib_logging.py

@@ -10,7 +10,7 @@ from io import StringIO
 import pytest
 
 from tqdm import tqdm
-from tqdm.contrib.logging import _get_first_found_console_logging_formatter
+from tqdm.contrib.logging import _get_first_found_console_logging_handler
 from tqdm.contrib.logging import _TqdmLoggingHandler as TqdmLoggingHandler
 from tqdm.contrib.logging import logging_redirect_tqdm, tqdm_logging_redirect
 
@@ -68,33 +68,25 @@ class TestTqdmLoggingHandler:
             logger.info('test')
 
 
-class TestGetFirstFoundConsoleLoggingFormatter:
+class TestGetFirstFoundConsoleLoggingHandler:
     def test_should_return_none_for_no_handlers(self):
-        assert _get_first_found_console_logging_formatter([]) is None
+        assert _get_first_found_console_logging_handler([]) is None
 
     def test_should_return_none_without_stream_handler(self):
         handler = logging.handlers.MemoryHandler(capacity=1)
-        handler.formatter = TEST_LOGGING_FORMATTER
+        assert _get_first_found_console_logging_handler([handler]) is None
-        assert _get_first_found_console_logging_formatter([handler]) is None
 
     def test_should_return_none_for_stream_handler_not_stdout_or_stderr(self):
         handler = logging.StreamHandler(StringIO())
-        handler.formatter = TEST_LOGGING_FORMATTER
+        assert _get_first_found_console_logging_handler([handler]) is None
-        assert _get_first_found_console_logging_formatter([handler]) is None
 
-    def test_should_return_stream_handler_formatter_if_stream_is_stdout(self):
+    def test_should_return_stream_handler_if_stream_is_stdout(self):
         handler = logging.StreamHandler(sys.stdout)
-        handler.formatter = TEST_LOGGING_FORMATTER
+        assert _get_first_found_console_logging_handler([handler]) == handler
-        assert _get_first_found_console_logging_formatter(
-            [handler]
-        ) == TEST_LOGGING_FORMATTER
 
-    def test_should_return_stream_handler_formatter_if_stream_is_stderr(self):
+    def test_should_return_stream_handler_if_stream_is_stderr(self):
         handler = logging.StreamHandler(sys.stderr)
-        handler.formatter = TEST_LOGGING_FORMATTER
+        assert _get_first_found_console_logging_handler([handler]) == handler
-        assert _get_first_found_console_logging_formatter(
-            [handler]
-        ) == TEST_LOGGING_FORMATTER
 
 
 class TestRedirectLoggingToTqdm:

tqdm/contrib/logging.py

@@ -26,7 +26,7 @@ class _TqdmLoggingHandler(logging.StreamHandler):
     def emit(self, record):
         try:
             msg = self.format(record)
-            self.tqdm_class.write(msg)
+            self.tqdm_class.write(msg, file=self.stream)
             self.flush()
         except (KeyboardInterrupt, SystemExit):
             raise
@@ -39,10 +39,10 @@ def _is_console_logging_handler(handler):
             and handler.stream in {sys.stdout, sys.stderr})
 
 
-def _get_first_found_console_logging_formatter(handlers):
+def _get_first_found_console_logging_handler(handlers):
     for handler in handlers:
         if _is_console_logging_handler(handler):
-            return handler.formatter
+            return handler
 
 
 @contextmanager
@@ -85,8 +85,10 @@ def logging_redirect_tqdm(
     try:
         for logger in loggers:
             tqdm_handler = _TqdmLoggingHandler(tqdm_class)
-            tqdm_handler.setFormatter(
+            orig_handler = _get_first_found_console_logging_handler(logger.handlers)
-                _get_first_found_console_logging_formatter(logger.handlers))
+            if orig_handler is not None:
+                tqdm_handler.setFormatter(orig_handler.formatter)
+                tqdm_handler.stream = orig_handler.stream
             logger.handlers = [
                 handler for handler in logger.handlers
                 if not _is_console_logging_handler(handler)] + [tqdm_handler]