google-calendar: Generalize the datetime parsing for event fields.

Moved the parsing logic into `get_start_or_end` to enable re-using the
function when we add support for the `end` field of event.

Author: Niloth-p

zulip/integrations/google/google-calendar

@@ -9,7 +9,7 @@ import sys
 import time
 from configparser import ConfigParser
 from dataclasses import dataclass
-from typing import List, Optional, Set, Tuple, TypedDict
+from typing import Any, Dict, List, Optional, Set, Tuple, TypedDict
 
 import dateutil.parser
 import pytz
@@ -212,31 +212,28 @@ def populate_events() -> Optional[None]:
 
     events.clear()
     for event in feed["items"]:
-        try:
-            start = dateutil.parser.parse(event["start"]["dateTime"])
-            # According to the API documentation, a time zone offset is required
-            # for start.dateTime unless a time zone is explicitly specified in
-            # start.timeZone.
-            if start.tzinfo is None:
-                event_timezone = pytz.timezone(event["start"]["timeZone"])
-                # pytz timezones include an extra localize method that's not part
-                # of the tzinfo base class.
-                start = event_timezone.localize(start)
-        except KeyError:
-            # All-day events can have only a date.
-            start_naive = dateutil.parser.parse(event["start"]["date"])
-
-            # All-day events don't have a time zone offset; instead, we use the
-            # time zone of the calendar.
-            calendar_timezone = pytz.timezone(feed["timeZone"])
-            # pytz timezones include an extra localize method that's not part
-            # of the tzinfo base class.
-            start = calendar_timezone.localize(start_naive)
+
+        def get_start_or_end(event: Dict[str, Any], field_name: str) -> datetime.datetime:
+            try:
+                field = dateutil.parser.parse(event[field_name]["dateTime"])
+                # a time zone offset is required unless timeZone is explicitly specified.
+                if field.tzinfo is None:
+                    # pytz timezones include an extra localize method that's not part
+                    # of the tzinfo base class.
+                    event_timezone = pytz.timezone(event[field_name]["timeZone"])
+                    field = event_timezone.localize(field)
+            except KeyError:
+                # All-day events can have only a date.
+                field_naive = dateutil.parser.parse(event[field_name]["date"])
+                # All-day events do not have a time zone offset; use the calendar's time zone.
+                calendar_timezone = pytz.timezone(feed["timeZone"])
+                field = calendar_timezone.localize(field_naive)
+            return field
 
         events.append(
             {
                 "id": event["id"],
-                "start": start,
+                "start": get_start_or_end(event, "start"),
                 "summary": event.get("summary", "(No Title)"),
             }
         )