[wip] Add PromptToolkitLogHandler.

examples/logging/colored_logs.py

@@ -0,0 +1,23 @@
+"""
+Example of a custom logging handler that uses prompt_toolkit to render nicely
+colored logs.
+"""
+import logging
+import time
+
+from prompt_toolkit.shortcuts.logging import PromptToolkitLogHandler
+
+
+def main() -> None:
+    logging.basicConfig(level=logging.DEBUG, handlers=[PromptToolkitLogHandler()])
+
+    for i in range(10):
+        logging.debug(f"test debug {i}")
+        logging.info(f"test info {i}")
+        logging.warning(f"test warning {i}")
+        logging.error(f"test error {i}")
+        time.sleep(0.5)
+
+
+if __name__ == "__main__":
+    main()

src/prompt_toolkit/shortcuts/logging.py

@@ -0,0 +1,74 @@
+"""
+Utility for printing colored logs.
+"""
+import datetime
+import logging
+from typing import Callable, Optional, TextIO, Union
+
+from prompt_toolkit.formatted_text import HTML
+from prompt_toolkit.layout.containers import AnyContainer, VSplit, Window
+from prompt_toolkit.layout.controls import FormattedTextControl
+from prompt_toolkit.styles import Style
+
+from .utils import print_container, print_formatted_text
+
+__all__ = ["PromptToolkitLogHandler"]
+
+
+def default_template(record: logging.LogRecord) -> HTML:
+    now = datetime.datetime.now()
+    return HTML(
+        f"<{record.levelname}>"
+        "<time>[{now}]</time> <level>{level:10}</level> <message>{msg}</message>"
+        f"</{record.levelname}>"
+    ).format(
+        now=now.strftime("%m/%d/%y %H:%M:%S"),
+        level=record.levelname,
+        msg=record.msg,
+    )
+
+
+def default_style() -> Style:
+    return Style.from_dict(
+        {
+            "time": "ansimagenta",
+            "warning": "#aa8888",
+            "warning level": "reverse",
+            "debug": "#888888",
+            "error": "ansired",
+            "error level": "reverse",
+            "info": "#00aa00",
+        }
+    )
+
+
+class PromptToolkitLogHandler(logging.StreamHandler):
+    """
+    Print all logging messages using the given template.
+
+    Usage::
+
+        import logging
+        logging.basicConfig(
+            level=logging.DEBUG,
+            handlers=[PromptToolkitHandler()]
+        )
+    """
+    # NOTE: Previously, I tried using `print_container` instead of
+    #       `print_formatted_text`. This doesn't work unfortunately, because
+    #       we'd try to create/access an event loop, which causes asyncio to
+    #       log new messages. We can't log anything while printing a log
+    #       message.
+
+    def __init__(
+        self,
+        template: Callable[[logging.LogRecord], HTML] = default_template,
+        style: Style = default_style(),
+        stream: Optional[TextIO] = None,
+    ) -> None:
+        self.template = template
+        self.style = style
+        super().__init__(stream=stream)
+
+    def emit(self, record) -> None:
+        print_formatted_text(self.template(record), style=self.style, file=self.stream)