logging.py — flask Source File

Source Code

from __future__ import annotations

import logging
import sys
import typing as t

from werkzeug.local import LocalProxy

from .globals import request

if t.TYPE_CHECKING:  # pragma: no cover
    from .sansio.app import App


@LocalProxy
def wsgi_errors_stream() -> t.TextIO:
    """Find the most appropriate error stream for the application. If a request
    is active, log to ``wsgi.errors``, otherwise use ``sys.stderr``.

    If you configure your own :class:`logging.StreamHandler`, you may want to
    use this for the stream. If you are using file or dict configuration and
    can't import this directly, you can refer to it as
    ``ext://flask.logging.wsgi_errors_stream``.
    """
    if request:
        return request.environ["wsgi.errors"]  # type: ignore[no-any-return]

    return sys.stderr


def has_level_handler(logger: logging.Logger) -> bool:
    """Check if there is a handler in the logging chain that will handle the
    given logger's :meth:`effective level <~logging.Logger.getEffectiveLevel>`.
    """
    level = logger.getEffectiveLevel()
    current = logger

    while current:
        if any(handler.level <= level for handler in current.handlers):
            return True

        if not current.propagate:
            break

        current = current.parent  # type: ignore

    return False


#: Log messages to :func:`~flask.logging.wsgi_errors_stream` with the format
#: ``[%(asctime)s] %(levelname)s in %(module)s: %(message)s``.
default_handler = logging.StreamHandler(wsgi_errors_stream)  # type: ignore
default_handler.setFormatter(
    logging.Formatter("[%(asctime)s] %(levelname)s in %(module)s: %(message)s")
)


def create_logger(app: App) -> logging.Logger:
    """Get the Flask app's logger and configure it if needed.

    The logger name will be the same as
    :attr:`app.import_name <flask.Flask.name>`.

    When :attr:`~flask.Flask.debug` is enabled, set the logger level to
    :data:`logging.DEBUG` if it is not set.

    If there is no handler for the logger's effective level, add a
    :class:`~logging.StreamHandler` for
    :func:`~flask.logging.wsgi_errors_stream` with a basic format.
    """
    logger = logging.getLogger(app.name)

    if app.debug and not logger.level:
        logger.setLevel(logging.DEBUG)

    if not has_level_handler(logger):
        logger.addHandler(default_handler)

    return logger