Add basic_logger utility

ska_helpers/logging.py

@@ -0,0 +1,92 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+
+__all__ = ['basic_logger']
+
+
+def basic_logger(name, format="%(asctime)s %(funcName)s: %(message)s", **kwargs):
+    """Create logger ``name`` using logging.basicConfig.
+
+    This is a thin wrapper around logging.basicConfig, except:
+
+    - Uses logger named ``name`` instead of the root logger
+    - Defaults to a standard format for Ska applications. Specify
+      ``format=None`` to use the default ``basicConfig`` format.
+    - Not recommended for multithreaded or multiprocess applications due to
+      using a temporary monkey-patch of a global variable to create the logger.
+      It will probably work but it is not guaranteed.
+
+    This function does nothing if the ``name`` logger already has handlers
+    configured, unless the keyword argument *force* is set to ``True``.
+    It is a convenience method intended to do one-shot creation of a logger.
+
+    The default behaviour is to create a StreamHandler which writes to
+    ``sys.stderr``, set a formatter using the format string ``"%(asctime)s
+    %(funcName)s: %(message)s"``, and add the handler to the ``name`` logger
+    with a level of WARNING.
+
+    Example::
+
+      # In __init__.py for a package or in any module
+      from ska_helpers.logging import basic_logger
+      logger = basic_logger(__name__, level='INFO')
+
+      # In other submodules within a package the normal usage is to inherit
+      # the package logger.
+      import logging
+      logger = logging.getLogger(__name__)
+
+    A number of optional keyword arguments may be specified, which can alter
+    the default behaviour.
+
+    filename  Specifies that a FileHandler be created, using the specified
+              filename, rather than a StreamHandler.
+    filemode  Specifies the mode to open the file, if filename is specified
+              (if filemode is unspecified, it defaults to 'a').
+    format    Use the specified format string for the handler.
+    datefmt   Use the specified date/time format.
+    style     If a format string is specified, use this to specify the
+              type of format string (possible values '%', '{', '$', for
+              %-formatting, :meth:`str.format` and :class:`string.Template`
+              - defaults to '%').
+    level     Set the ``name`` logger level to the specified level. This can be
+              a number (10, 20, ...) or a string ('NOTSET', 'DEBUG', 'INFO',
+              'WARNING', 'ERROR', 'CRITICAL') or ``logging.DEBUG``, etc.
+    stream    Use the specified stream to initialize the StreamHandler. Note
+              that this argument is incompatible with 'filename' - if both
+              are present, 'stream' is ignored.
+    handlers  If specified, this should be an iterable of already created
+              handlers, which will be added to the ``name`` handler. Any handler
+              in the list which does not have a formatter assigned will be
+              assigned the formatter created in this function.
+    force     If this keyword  is specified as true, any existing handlers
+              attached to the ``name`` logger are removed and closed, before
+              carrying out the configuration as specified by the other
+              arguments.
+    Note that you could specify a stream created using open(filename, mode)
+    rather than passing the filename and mode in. However, it should be
+    remembered that StreamHandler does not close its stream (since it may be
+    using sys.stdout or sys.stderr), whereas FileHandler closes its stream
+    when the handler is closed.
+
+    Note this function is probably not thread-safe.
+
+    :param name: str, logger name
+    :param format: str, format string for handler
+    :param **kwargs: other keyword arguments for logging.basicConfig
+    :returns: Logger object
+    """
+    import logging
+
+    if format is not None:
+        kwargs['format'] = format
+    logger = logging.getLogger(name)
+
+    # Monkeypatch logging temporarily and configure our logger
+    root = logging.root
+    try:
+        logging.root = logger
+        logging.basicConfig(**kwargs)
+    finally:
+        logging.root = root
+
+    return logger

ska_helpers/utils.py

@@ -1,3 +1,5 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+
 import functools
 
 __all__ = ['LazyDict', 'LazyVal']