changed prints for logs and sys.exit for exceptions

tweet_model/tweet_model.py

 # -*- coding: utf-8 -*-
 """Main module."""
 
+import logging
 import sys
 
 from tweet_manager.lib import format_csv
 
+# Configure logger
+LOG_FORMAT = '[%(asctime)-15s] %(levelname)s: %(message)s'
+logging.basicConfig(level=logging.DEBUG, format=LOG_FORMAT)
+logger = logging.getLogger("logger")
+
 
 class Tweet():
     """
@@ -358,6 +364,10 @@ class Tweet():
         return getattr(self, key)
 
 
+class NotValidTweetError(Exception):
+    pass
+
+
 def get_tweets_from_csv(csv_file):
     """
     Take one argument: a path pointing to a valid CSV file.
@@ -385,9 +395,11 @@ def get_tweets_from_csv(csv_file):
         for component in field_components:
             error_string += component
             if (checking_dict is None) or (component not in checking_dict):
-                print('The field in the header "' + error_string + '" is ' +
-                      'not a valid element of a Tweet')
-                sys.exit(1)
+                logger.error('The field in the header "{error_string}" ' +
+                             'is not a valid element of a Tweet')
+                raise NotValidTweetError("Header contains field which doesn't"
+                                         + " belong to tweet specification: "
+                                         + error_string)
             checking_dict = checking_dict[component]
             error_string += "."