timetags: make timetags lazy

lumicks/pylake/channel.py

@@ -917,12 +917,26 @@ class TimeTags:
 
     def __init__(self, data, start=None, stop=None):
         self._src_data = data
-        self.start = start if start is not None else (self.data[0] if self.data.size > 0 else 0)
-        self.stop = stop if stop is not None else (self.data[-1] + 1 if self.data.size > 0 else 0)
+        self._start = start
+        self._stop = stop
 
     def __len__(self):
         return self.data.size
 
+    @property
+    def start(self):
+        return (
+            self._start if self._start is not None else (self.data[0] if self.data.size > 0 else 0)
+        )
+
+    @property
+    def stop(self):
+        return (
+            self._stop
+            if self._stop is not None
+            else (self.data[-1] + 1 if self.data.size > 0 else 0)
+        )
+
     @property
     def data(self):
         return np.asarray(self._src_data)

lumicks/pylake/tests/test_file/test_caching.py

@@ -47,9 +47,8 @@ def test_global_cache_timetags(h5_file):
     if pylake.File.from_h5py(h5_file).format_version == 2:
         _get_array.cache_clear()
         tags1 = pylake.File.from_h5py(h5_file)["Photon Time Tags"]["Red"]
-        assert _get_array.cache_info().hits == 3  # start and stop pull the data every time
         tags2 = pylake.File.from_h5py(h5_file)["Photon Time Tags"]["Red"]
-        assert _get_array.cache_info().hits == 6
+        assert _get_array.cache_info().hits == 0
 
         # These should point to the same data
         assert id(tags1.data) == id(tags2.data)