refactoring: move the message logger setup out of main()

Eventually we will want to use this code in other sample applications,
so let's move the logger configuration code to a separate function.

There's a bit of ugly hacking in this current implementation because
I've added variable members to logging.logger.  These are actaully
config-once variables that convey the logging directory and filename.
I did not want to add more names to the global namespace, so I hacked
a temporary solution in which logging.logger is acts as a conveyor and
private namespace.  We'll get that cleaned up as we do more refactoring.

examples/classifier_compression/compress_classifier.py

@@ -79,11 +79,7 @@ from distiller.data_loggers import TensorBoardLogger, PythonLogger, ActivationSp
 import distiller.quantization as quantization
 from models import ALL_MODEL_NAMES, create_model
 
-
 msglogger = None
-log_filename = ''
-
-
 parser = argparse.ArgumentParser(description='Distiller image classification model compression')
 parser.add_argument('data', metavar='DIR', help='path to dataset')
 parser.add_argument('--arch', '-a', metavar='ARCH', default='resnet18',
@@ -134,22 +130,26 @@ parser.add_argument('--gpus', metavar='DEV_ID', default=None,
 parser.add_argument('--name', '-n', metavar='NAME', default=None, help='Experiment name')
 
 
-def main():
-
-    args = parser.parse_args()
-
+def config_logger(experiment_name):
     # The Distiller library writes logs to the Python logger, so we configure it.
-    global msglogger
     timestr = time.strftime("%Y.%m.%d-%H%M%S")
-    filename = timestr if args.name is None else args.name + '___' + timestr
+    filename = timestr if experiment_name is None else experiment_name + '___' + timestr
     logdir = './logs' + '/' + filename
     if not os.path.exists(logdir):
         os.makedirs(logdir)
     log_filename = os.path.join(logdir, filename + '.log')
     logging.config.fileConfig(os.path.join(script_dir, 'logging.conf'), defaults={'logfilename': log_filename})
     msglogger = logging.getLogger()
-
+    msglogger.logdir = logdir
+    msglogger.log_filename = log_filename
     msglogger.info('Log file for this run: ' + os.path.realpath(log_filename))
+    return msglogger
+
+
+def main():
+    global msglogger
+    args = parser.parse_args()
+    msglogger = config_logger(args.name)
 
     # Log various details about the execution environment.  It is sometimes useful
     # to refer to past experiment executions and this information may be useful.
@@ -202,7 +202,7 @@ def main():
     compression_scheduler = None
     # Create a couple of logging backends.  TensorBoardLogger writes log files in a format
     # that can be read by Google's Tensor Board.  PythonLogger writes to the Python logger.
-    tflogger = TensorBoardLogger(logdir)
+    tflogger = TensorBoardLogger(msglogger.logdir)
     pylogger = PythonLogger(msglogger)
 
     # We can optionally resume from a checkpoint
@@ -506,4 +506,4 @@ if __name__ == '__main__':
     finally:
         if msglogger is not None:
             msglogger.info('')
-            msglogger.info('Log file for this run: ' + os.path.realpath(log_filename))
+            msglogger.info('Log file for this run: ' + os.path.realpath(msglogger.log_filename))