Replace "print" logging with the "logging" module

This commit rewrites the make-shift "log" methods to use the logging
framework without requiring changes to the callers.  This will be done
in a latter commit to keep things reviewable.

Signed-off-by: Niels Thykier <niels@thykier.net>

britney.py

@@ -179,6 +179,7 @@ does for the generation of the update excuses.
 
  * The excuses are written in an HTML file.
 """
+import logging
 import optparse
 import os
 import sys
@@ -253,6 +254,32 @@ class Britney(object):
         the information needed by the other methods of the class.
         """
 
+        # setup logging - provide the "short level name" (i.e. INFO -> I) that
+        # we used to use prior to using the logging module.
+
+        old_factory = logging.getLogRecordFactory()
+        short_level_mapping = {
+            'CRITIAL': 'F',
+            'INFO': 'I',
+            'WARNING': 'W',
+            'ERROR': 'E',
+            'DEBUG': 'N',
+        }
+
+        def record_factory(*args, **kwargs):
+            record = old_factory(*args, **kwargs)
+            try:
+                record.shortlevelname = short_level_mapping[record.levelname]
+            except KeyError:
+                record.shortlevelname = record.levelname
+            return record
+
+        logging.setLogRecordFactory(record_factory)
+        logging.basicConfig(format='{shortlevelname}: [{asctime}] - {message}', style='{',
+                            datefmt="%Y-%m-%dT%H:%M:%S%z")
+
+        self.logger = logging.getLogger()
+
         # parse the command line arguments
         self.policies = []
         self._hint_parser = HintParser(self)
@@ -416,6 +443,11 @@ class Britney(object):
                           help="Do not compute which packages can migrate.")
         (self.options, self.args) = parser.parse_args()
 
+        if self.options.verbose:
+            self.logger.setLevel(logging.INFO)
+        else:
+            self.logger.setLevel(logging.WARNING)
+        
         # integrity checks
         if self.options.nuninst_cache and self.options.print_uninst:  # pragma: no cover
             self.log("nuninst_cache and print_uninst are mutually exclusive!", type="E")
@@ -529,8 +561,12 @@ class Britney(object):
         `Error'. Warnings and errors are always printed, and information is
         printed only if verbose logging is enabled.
         """
-        if self.options.verbose or type in ("E", "W"):
-            print("%s: [%s] - %s" % (type, time.asctime(), msg))
+        level = {
+            'I': logging.INFO,
+            'W': logging.WARNING,
+            'E': logging.ERROR,
+        }.get(type, logging.INFO)
+        self.logger.log(level, msg)
 
     def _load_faux_packages(self, faux_packages_file):
         """Loads fake packages
@@ -2771,6 +2807,7 @@ class Britney(object):
                     self.log('>   %s' % stat, type="I")
         else:
             self.log('Migration computation skipped as requested.', type='I')
+        logging.shutdown()
 
 
 if __name__ == '__main__':

britney2/policies/policy.py

@@ -1,4 +1,5 @@
 import json
+import logging
 import os
 import time
 from abc import abstractmethod
@@ -30,6 +31,8 @@ class BasePolicy(object):
         self.suite_info = suite_info
         self.applicable_suites = applicable_suites
         self.hints = None
+        logger_name = ".".join((self.__class__.__module__, self.__class__.__name__))
+        self.logger = logging.getLogger(logger_name)
 
     # FIXME: use a proper logging framework
     def log(self, msg, type="I"):
@@ -41,8 +44,12 @@ class BasePolicy(object):
         `Error'. Warnings and errors are always printed, and information is
         printed only if verbose logging is enabled.
         """
-        if self.options.verbose or type in ("E", "W"):
-            print("%s: [%s] - %s" % (type, time.asctime(), msg))
+        level = {
+            'I': logging.INFO,
+            'W': logging.WARNING,
+            'E': logging.ERROR,
+        }.get(type, logging.INFO)
+        self.logger.log(level, msg)
 
     def register_hints(self, hint_parser):  # pragma: no cover
         """Register new hints that this policy accepts