journal: allow JournalHandler constructor to be called with args in a positional param

This change enables to add extra fields to JournalHandler in a
configuration file loaded by `logging.config.fileConfig`, which only allows positional
parameters:

class=systemd.journal.JournalHandler
args={'level': INFO, 'SYSLOG_IDENTIFIER': 'my-cool-app'}

[zj: originally the patch added a new positional parameter to
__init__(), but that is not backwards compatible. So I added a new
classmethod to allow the positional parameters to be passed.]

Author: otamachan

systemd/journal.py

@@ -565,6 +565,20 @@ def __init__(self, level=_logging.NOTSET, sender_function=send, **kwargs):
         self.send = sender_function
         self._extra = kwargs
 
+    @classmethod
+    def with_args(cls, config=None):
+        """Create a JournalHandler with a configuration dictionary
+
+        This creates a JournalHandler instance, but accepts the parameters through
+        a dictionary that can be specified as a positional argument. This is useful
+        in contexts like logging.config.fileConfig, where the syntax does not allow
+        for positional arguments.
+
+        >>> JournalHandler.with_args({'SYSLOG_IDENTIFIER':'my-cool-app'})
+        <...JournalHandler ...>
+        """
+        return cls(**(config or {}))
+
     def emit(self, record):
         """Write `record` as a journal event.
 

systemd/test/test_journal.py

@@ -82,10 +82,14 @@ def test_journalhandler_init_exception():
     kw = {' X  ':3}
     with pytest.raises(ValueError):
         journal.JournalHandler(**kw)
+    with pytest.raises(ValueError):
+        journal.JournalHandler.with_args(kw)
 
 def test_journalhandler_init():
     kw = {'X':3, 'X3':4}
     journal.JournalHandler(logging.INFO, **kw)
+    kw['level'] = logging.INFO
+    journal.JournalHandler.with_args(kw)
 
 def test_journalhandler_info():
     record = logging.LogRecord('test-logger', logging.INFO, 'testpath', 1, 'test', None, None)
@@ -98,6 +102,16 @@ def test_journalhandler_info():
     assert 'X=3' in sender.buf[0]
     assert 'X3=4' in sender.buf[0]
 
+    sender = MockSender()
+    handler = journal.JournalHandler.with_args({'level':logging.INFO, 'X':3, 'X3':4, 'sender_function':sender.send})
+    handler.emit(record)
+    assert len(sender.buf) == 1
+    assert 'X=3' in sender.buf[0]
+    assert 'X3=4' in sender.buf[0]
+
+    # just check that args==None doesn't cause an error
+    journal.JournalHandler.with_args()
+
 def test_journalhandler_no_message_id():
     record = logging.LogRecord('test-logger', logging.INFO, 'testpath', 1, 'test', None, None)
     sender = MockSender()