Define datetime min and max as constants

Change the way the markers are represented in RingBuffer
so that `replace()` is not called every time the markers
are assigned or compared to.

Signed-off-by: Daniel Zullo <[email protected]>

Author: daniel-zullo-frequenz

src/frequenz/sdk/timeseries/_ringbuffer.py

@@ -46,6 +46,9 @@ def contains(self, timestamp: datetime) -> bool:
 class OrderedRingBuffer(Generic[FloatArray]):
     """Time aware ringbuffer that keeps its entries sorted by time."""
 
+    _DATETIME_MIN = datetime.min.replace(tzinfo=timezone.utc)
+    _DATETIME_MAX = datetime.max.replace(tzinfo=timezone.utc)
+
     def __init__(
         self,
         buffer: FloatArray,
@@ -76,8 +79,8 @@ def __init__(
         self._time_index_alignment: datetime = time_index_alignment
 
         self._gaps: list[Gap] = []
-        self._datetime_newest: datetime = datetime.min.replace(tzinfo=timezone.utc)
-        self._datetime_oldest: datetime = datetime.max.replace(tzinfo=timezone.utc)
+        self._datetime_newest: datetime = self._DATETIME_MIN
+        self._datetime_oldest: datetime = self._DATETIME_MAX
         self._time_range: timedelta = (len(self._buffer) - 1) * sampling_period
 
     @property
@@ -132,7 +135,7 @@ def update(self, sample: Sample) -> None:
         # Don't add outdated entries
         if (
             timestamp < self._datetime_oldest
-            and self._datetime_oldest != datetime.max.replace(tzinfo=timezone.utc)
+            and self._datetime_oldest != self._DATETIME_MAX
         ):
             raise IndexError(
                 f"Timestamp {timestamp} too old (cut-off is at {self._datetime_oldest})."
@@ -488,7 +491,7 @@ def __len__(self) -> int:
         Returns:
             The length.
         """
-        if self._datetime_newest == datetime.min.replace(tzinfo=timezone.utc):
+        if self._datetime_newest == self._DATETIME_MIN:
             return 0
 
         start_index = self.datetime_to_index(self._datetime_oldest)