sun_moon.py: Allow DST adjustment to rise/set times.

astronomy/README.md

@@ -184,6 +184,13 @@ Variants:
  `time.time()`.
 * 2 Return text of form hh:mm:ss (or --:--:--) being local time (`LT`).
 
+If bit 2 of `variant` is set and a `dst` constructor arg has been passed, the
+`dst` function will be applied to the result. This caters for the case where the
+machine clock runs winter time and a dst-adjusted result is required. It should
+be noted that applying dst adjustment to a time close to midnight can result in
+rollover, i.e. a time > 24:00. Handling this case is the responsibility of the
+application.
+
 Example constructor invocations:
 ```python
 r = RiSet()  # UK near Manchester

astronomy/sun_moon.py

@@ -319,11 +319,14 @@ class RiSet:
                     self._times[idx] = n
 
     def _format(self, n, variant):
+        if (n is not None) and (variant & 4):  # Machine clock set to UTC
+            variant &= 0x03
+            n = self.dst(n + self._t0) - self._t0
         if variant == 0:  # Default: secs since Midnight (local time)
             return n
         elif variant == 1:  # Secs since epoch of MicroPython platform
             return None if n is None else n + self._t0
-        # variant == 3
+        # variant == 2
         if n is None:
             return "--:--:--"
         else: