Print exceptions with stack trace

lib/tfw/config/log.py

@@ -1,6 +1,8 @@
 # pylint: disable=bad-whitespace
 from sys import stderr
+from collections import deque
 from datetime import datetime
+from traceback import format_exception, walk_tb
 from logging import DEBUG, getLogger, Handler, Formatter, Filter
 
 TFW_LOG_PATH = '/var/log/tfw.log'
@@ -71,6 +73,10 @@ class TFWLogFormatter(Formatter):
         'NOTSET'   : COLOR.CYAN
     }
 
+    def __init__(self):
+        self.last_trace = None
+        super().__init__()
+
     def format(self, record):
         date = datetime.utcfromtimestamp(record.created).strftime('%H:%M:%S')
         if record.args:
@@ -82,10 +88,23 @@ class TFWLogFormatter(Formatter):
             short_message = record.msg
             long_message = record.msg
 
+        if record.exc_info:
+            current_trace = self.fetch_exception_origin(record.exc_info[2])
+            if current_trace != self.last_trace:
+                self.last_trace = current_trace
+                trace = '\n'+''.join(format_exception(*record.exc_info))
+            else:
+                trace = (f'\nSee previous traceback...\n'
+                         f'{record.exc_info[0].__name__}: {record.exc_info[1]}')
+        else:
+            trace = ''
+
         short_entry = (f'[{COLOR.GREY}{date}{COLOR.RESET}|>'
                        f'{self.severity[record.levelname]}{record.module}:'
-                       f'{record.levelname.lower()}{COLOR.RESET}] {short_message}')
-        long_entry = f'[{date}|>{record.module}:{record.levelname.lower()}] {long_message}'
+                       f'{record.levelname.lower()}{COLOR.RESET}] {short_message}'
+                       f'{trace}')
+        long_entry = (f'[{date}|>{record.module}:{record.levelname.lower()}] '
+                      f'{long_message}{trace}')
         return short_entry, long_entry
 
     def trim(self, value, in_dict=False):
@@ -97,6 +116,10 @@ class TFWLogFormatter(Formatter):
         value_str = str(value)
         return value_str if len(value_str) <= 20 else f'{value_str[:20]}...'
 
+    @staticmethod
+    def fetch_exception_origin(trace):
+        return deque(walk_tb(trace), maxlen=1).pop()
+
 
 class TFWLogWhitelistFilter(Filter):
     def __init__(self, names):