Allow parsing datetime string without explicit UTC offset (timezone)

Fixes #299

Lib/glyphsLib/types.py

@@ -223,12 +223,24 @@ def plistValue(self):
 class glyphs_datetime(baseType):
     """Read/write a datetime.  Doesn't maintain time zone offset."""
 
+    utc_offset_re = re.compile(
+        r".* (?P<sign>\+|\-)(?P<hours>\d\d)(?P<minutes>\d\d)$")
+
     def read(self, src):
-        src = src.replace('"', '')
         """Parse a datetime object from a string."""
+        string = src.replace('"', '')
         # parse timezone ourselves, since %z is not always supported
         # see: http://bugs.python.org/issue6641
-        string, tz = src.rsplit(' ', 1)
+        m = glyphs_datetime.utc_offset_re.match(string)
+        if m:
+            sign = 1 if m.group("sign") == "+" else -1
+            tz_hours = sign * int(m.group("hours"))
+            tz_minutes = sign * int(m.group("minutes"))
+            offset = datetime.timedelta(hours=tz_hours, minutes=tz_minutes)
+            string = string[:-6]
+        else:
+            # no explicit timezone
+            offset = datetime.timedelta(0)
         if 'AM' in string or 'PM' in string:
             datetime_obj = datetime.datetime.strptime(
                 string, '%Y-%m-%d %I:%M:%S %p'
@@ -237,8 +249,6 @@ def read(self, src):
             datetime_obj = datetime.datetime.strptime(
                 string, '%Y-%m-%d %H:%M:%S'
             )
-        offset = datetime.timedelta(
-            hours=int(tz[:3]), minutes=int(tz[0] + tz[3:]))
         return datetime_obj + offset
 
     def plistValue(self):

tests/types_test.py

@@ -39,6 +39,26 @@ def test_parsing_12hr_format(self):
         self.assertEqual(test_time.read(string_12hrs),
                          datetime.datetime(2017, 1, 1, 17, 30, 30))
 
+    def test_parsing_timezone(self):
+        """Assert glyphs_datetime can parse the (optional) timezone
+        formatted as UTC offset. If it's not explicitly specified, then
+        +0000 is assumed.
+        """
+        self.assertEqual(glyphs_datetime().read('2017-12-18 16:45:31 -0100'),
+                         datetime.datetime(2017, 12, 18, 15, 45, 31))
+
+        self.assertEqual(glyphs_datetime().read('2017-12-18 14:15:31 +0130'),
+                         datetime.datetime(2017, 12, 18, 15, 45, 31))
+
+        self.assertEqual(glyphs_datetime().read('2017-12-18 15:45:31'),
+                         datetime.datetime(2017, 12, 18, 15, 45, 31))
+
+        self.assertEqual(glyphs_datetime().read('2017-12-18 03:45:31 PM'),
+                         datetime.datetime(2017, 12, 18, 15, 45, 31))
+
+        self.assertEqual(glyphs_datetime().read('2017-12-18 09:45:31 AM'),
+                         datetime.datetime(2017, 12, 18, 9, 45, 31))
+
 
 if __name__ == '__main__':
     unittest.main()