Outputs cache, clear and interpolate data

Preparation to solve build new scheduling algorithm. See #78 (closed).

Use the ping mechanism to let outputs know their targets.

Outputs record pull time per target to determine data to store/clear. Store data, and clear after pull what can't be pulled anymore with strictly increasing pull time per target.

Outputs do nearest interpolation on pull and throw an arror when out of the data range.

Fixes #76 (closed)

src/finam/sdk/adapter.py

@@ -106,6 +106,22 @@ class Adapter(IAdapter, Input, Output, ABC):
 
     @final
     def get_data(self, time, target):
+        """Get the transformed data of this adapter.
+
+        Internally calls :meth:`._get_data`.
+
+        Parameters
+        ----------
+        time : datetime.datatime
+            Simulation time to get the data for.
+        target : IInput
+            Requesting end point of this pull.
+
+        Returns
+        -------
+        :class:`xarray.DataArray`
+            Transformed data-set for the requested time.
+        """
         self.logger.debug("get data")
         if not isinstance(time, datetime):
             with ErrorLogger(self.logger):
@@ -128,8 +144,13 @@ class Adapter(IAdapter, Input, Output, ABC):
         ----------
         time : datetime.datatime
             Simulation time to get the data for.
-        target : IInput or None
+        target : IInput
             Requesting end point of this pull.
+
+        Returns
+        -------
+        :class:`xarray.DataArray`
+            Transformed data-set for the requested time.
         """
         raise NotImplementedError(
             f"Method `_get_data` must be implemented by all adapters, but implementation is missing in {self.name}."