Avoid AmbiguousTimeError errors at end of DST

Signed-off-by: Jim Easterbrook <jim@jim-easterbrook.me.uk>

src/pywws/Plot.py

@@ -464,6 +464,9 @@
 import sys
 import xml.dom.minidom
 
+import pytz
+
+from .constants import HOUR
 from .conversions import *
 from . import DataStore
 from . import Localisation
@@ -520,12 +523,19 @@ def __init__(self, params, status, raw_data, hourly_data,
         if not os.path.isdir(self.work_dir):
             os.makedirs(self.work_dir)
 
+    def _local_offset(self, time):
+        try:
+            result = Local.utcoffset(time)
+        except pytz.AmbiguousTimeError:
+            result = Local.utcoffset(time + HOUR)
+        return result
+
     def _eval_time(self, time_str):
         # get timestamp of last data item
         result = self.hourly_data.before(datetime.max)
         if not result:
             result = datetime.utcnow()    # only if no hourly data
-        result += Local.utcoffset(result)
+        result += self._local_offset(result)
         # set to start of the day
         result = result.replace(hour=0, minute=0, second=0, microsecond=0)
         # apply time string
@@ -567,7 +577,7 @@ def DoPlot(self, input_file, output_file):
             self.x_hi = self.hourly_data.before(datetime.max)
             if not self.x_hi:
                 self.x_hi = datetime.utcnow()    # only if no hourly data
-            self.x_hi += Local.utcoffset(self.x_hi)
+            self.x_hi += self._local_offset(self.x_hi)
             if self.duration < timedelta(hours=6):
                 # set end of graph to start of the next minute after last item
                 self.x_hi += timedelta(seconds=55)
@@ -577,7 +587,7 @@ def DoPlot(self, input_file, output_file):
                 self.x_hi += timedelta(minutes=55)
                 self.x_hi = self.x_hi.replace(minute=0, second=0)
             self.x_lo = self.x_hi - self.duration
-        self.utcoffset = Local.utcoffset(self.x_hi)
+        self.utcoffset = self._local_offset(self.x_hi)
         # open gnuplot command file
         self.tmp_files = []
         cmd_file = os.path.join(self.work_dir, 'plot.cmd')

src/pywws/__init__.py

@@ -1,3 +1,3 @@
-__version__ = '15.10.0.dev1314'
-_release = '1314'
-_commit = 'b44bfff'
+__version__ = '15.10.0.dev1315'
+_release = '1315'
+_commit = 'ef2bb67'