Use a logger rather than print statements.

Unfortunately, bottle.py logs to stderr/stdout on its own.

icalendar_timeseries_server/api.py

@@ -1,8 +1,7 @@
 from typing import List
 
 import json
-from urllib.error import HTTPError
+import logging
-import traceback
 
 import bottle
 
@@ -26,7 +25,7 @@ def prometheus_api():
             'error': str(e)
         }
         bottle.response.status = 400
-        traceback.print_exc()
+        logging.exception('Cannot parse PromQL query')
         bottle.response.add_header('Content-Type', 'application/json')
         return json.dumps(response)
 
@@ -42,14 +41,6 @@ def prometheus_api():
                 'result': [e.serialize() for e in events]
             }
         }
-    except HTTPError as e:
-        response = {
-            'status': 'error',
-            'errorType': 'internal',
-            'error': str(e)
-        }
-        bottle.response.status = 500
-        traceback.print_exc()
     except BaseException:
         response = {
             'status': 'error',
@@ -57,7 +48,7 @@ def prometheus_api():
             'error': 'An internal error occurred.'
         }
         bottle.response.status = 500
-        traceback.print_exc()
+        logging.exception('An internal error occurred')
 
     bottle.response.add_header('Content-Type', 'application/json')
     return json.dumps(response)

icalendar_timeseries_server/cal.py

@@ -2,6 +2,7 @@ from typing import Dict, List, Iterable
 
 import sys
 import urllib.request
+import logging
 from datetime import datetime, date, timedelta
 from threading import Lock, Timer
 
@@ -54,8 +55,12 @@ def _scrape_calendar(name: str, config: CalendarConfig, start: datetime, end: da
     events = []
 
     opener: urllib.request.OpenerDirector = config.get_url_opener()
+    try:
         with opener.open(config.url) as response:
             data = response.read().decode('utf-8')
+    except BaseException:
+        logging.exception(f'An error occurred while scraping the calendar endpoint "{name}" ({config.url})')
+        return
     calendar = cal.Calendar.from_ical(data)
 
     for element in calendar.walk():

icalendar_timeseries_server/config.py

@@ -6,6 +6,7 @@ from datetime import timedelta
 import ssl
 import urllib.request
 import sys
+import logging
 
 import pytz
 import jinja2
@@ -155,7 +156,7 @@ def _keycheck(key: str,
         raise KeyError(f'Expected member "{key}" not found at path {path}')
     value: Any = config[key]
     if not isinstance(value, typ):
-        raise TypeError(f'Expected {typ}, not {type(value).__name__} for path {path}.{key}')
+        raise TypeError(f'Expected {typ.__name__}, not {type(value).__name__} for path {path}.{key}')
     if valid_values is not None:
         if value not in valid_values:
             raise ValueError(f'Expected one of {", ".join(valid_values)} ({typ}), not {value} for path {path}.{key}')
@@ -216,10 +217,17 @@ def get_jenv() -> jinja2.Environment:
 
 def load_config(filename: str):
     global CONFIG, JENV
+    try:
         with open(filename, 'r') as f:
             json_config = json.loads(f.read())
         CONFIG = Config(json_config)
         JENV = jinja2.Environment()
+    except json.JSONDecodeError as e:
+        logging.exception('Cannot parse config JSON')
+        raise e
+    except Exception as e:
+        logging.error(e)
+        raise e
 
 
 def load_default_config():

icalendar_timeseries_server/main.py

@@ -1,4 +1,5 @@
 import sys
+import logging
 
 import bottle
 
@@ -11,17 +12,32 @@ from icalendar_timeseries_server.api import prometheus_api
 
 
 def main():
+    # Set up logger
+    log_handler = logging.StreamHandler()
+    log_handler.setFormatter(logging.Formatter(
+        '%(asctime)s %(filename)s:%(lineno)d(%(funcName)s) [%(levelname)s]: %(message)s'))
+    logging.getLogger().addHandler(log_handler)
+
+    # Load configuration
+    config = get_config()
+    try:
         if len(sys.argv) == 1:
             load_default_config()
         elif len(sys.argv) == 2:
             load_config(sys.argv[1])
         else:
-        print(f'Can only read one config file, got "{" ".join(sys.argv[1:])}"')
+            logging.log(logging.FATAL, f'Can only read one config file, got "{" ".join(sys.argv[1:])}"')
             exit(1)
+        # Re-fetch config after parsing
         config = get_config()
+    except:
+        logging.fatal('Could not parse configuration file')
+        exit(1)
+
     # Schedule calendar scraping in the background
     for calname in config.calendars.keys():
         start_scrape_calendar(calname, config.calendars[calname])
+
     # Start the Bottle HTTP server
     bottle.run(host=config.addr, port=get_config().port)
 

icalendar_timeseries_server/query.py

@@ -1,6 +1,7 @@
 from typing import Dict
 
 import re
+import logging
 
 LABEL_MATCH_OPERATORS = [
     '=',
@@ -64,7 +65,7 @@ class MetricQuery:
         self.__parse(q)
 
     def __parse(self, q: str):
-        print(q)
+        logging.debug(f'Parsing PromQL query string: {q}')
         # globalstate:
         #   0 = parsing metric name
         #   1 = parsing filters