Several fixes

A container branch for the fixes of several issues I encountered while rolling out the current SaQC on the SEEFO pipeline.

Not sure, if this needs a real review, but as some of the changes touched code I am not completely familiar with, maybe you, @palmb and @luenensc want to have a look anyhow?

saqc/core/flags.py

 #!/usr/bin/env python
-
 from __future__ import annotations
 
 import pandas as pd
@@ -45,7 +44,6 @@ class _HistAccess:
         History._validateHistWithMask(value.hist, value.mask)
 
         self.obj._data[key] = value
-        self.obj._cache.pop(key, None)
 
 
 class Flags:
@@ -175,14 +173,8 @@ class Flags:
         # with python 3.7 dicts are insertion-ordered by default
         self._data = self._initFromRaw(raw_data, copy)
 
-        # this is a simple cache that reduce the calculation of the flags
-        # from the entire history of a flag column. The _cache is filled
-        # with __getitem__ and cleared on any write access to self_data.
-        # There are not to may write access possibilities here so we don't
-        # have to much trouble.
-        self._cache = {}
-
-    def _initFromRaw(self, data, copy) -> Dict[str, History]:
+    @staticmethod
+    def _initFromRaw(data: Mapping, copy: bool) -> Dict[str, History]:
         """
         init from dict-like: keys are flag column, values become
         initial columns of history(s).
@@ -250,16 +242,12 @@ class Flags:
         if not len(value) == len(self):
             raise ValueError("index must match current index in length")
 
-        _data, _cache = {}, {}
+        _data = {}
 
         for old, new in zip(self.columns, value):
             _data[new] = self._data[old]
 
-            if old in self._cache:
-                _cache[new] = self._cache[old]
-
         self._data = _data
-        self._cache = _cache
 
     @property
     def empty(self) -> bool:
@@ -283,11 +271,7 @@ class Flags:
     # item access
 
     def __getitem__(self, key: str) -> pd.Series:
-
-        if key not in self._cache:
-            self._cache[key] = self._data[key].max()
-
-        return self._cache[key].copy()
+        return self._data[key].max()
 
     def __setitem__(self, key: SelectT, value: ValueT):
         # force-KW is internal available only
@@ -330,11 +314,9 @@ class Flags:
             self._data[key] = History()
 
         self._data[key].append(value, force=True)
-        self._cache.pop(key, None)
 
     def __delitem__(self, key):
         self._data.pop(key)
-        self._cache.pop(key, None)
 
     def drop(self, key: str):
         """
@@ -418,8 +400,8 @@ class Flags:
         """
         di = dios.DictOfSeries(columns=self.columns)
 
-        for k, v in self._data.items():
-            di[k] = self[k]  # use cache
+        for k in self._data.keys():
+            di[k] = self[k]
 
         return di.copy()