Merge remote-tracking branch 'origin/improve-types' into abstract-cla…

…sses

# Conflicts:
#	cfgrib/abc.py
#	cfgrib/messages.py

.github/workflows/on-push.yml

@@ -81,7 +81,7 @@ jobs:
     - name: Type check with mypy
       shell: bash -l {0}
       run: |
-        mypy --strict cfgrib
+        mypy --strict cfgrib tests/test_*py
 
   code-style:
     runs-on: ubuntu-latest

cfgrib/messages.py

@@ -238,9 +238,9 @@ def itervalues(self) -> T.Iterator[Message]:
                             raise EOFError("No valid message found: %r" % self.filestream.path)
                         break
                     except Exception:
-                        if errors == "ignore":
+                        if self.errors == "ignore":
                             pass
-                        elif errors == "raise":
+                        elif self.errors == "raise":
                             raise
                         else:
                             LOG.exception("skipping corrupted Message")
@@ -399,3 +399,55 @@ def from_indexpath_or_filestream(
             log.exception("Can't read index file %r", indexpath)
 
         return cls.from_filestream(filestream, index_keys)
+
+    def __iter__(self) -> T.Iterator[str]:
+        return iter(self.index_keys)
+
+    def __len__(self) -> int:
+        return len(self.index_keys)
+
+    @property
+    def header_values(self) -> T.Dict[str, T.List[T.Any]]:
+        if not hasattr(self, "_header_values"):
+            all_header_values = {}  # type: T.Dict[str, T.Dict[T.Any, None]]
+            for header_values, _ in self.offsets:
+                for i, value in enumerate(header_values):
+                    values = all_header_values.setdefault(self.index_keys[i], {})
+                    if value not in values:
+                        values[value] = None
+            self._header_values = {k: list(v) for k, v in all_header_values.items()}
+        return self._header_values
+
+    def __getitem__(self, item: str) -> T.List[T.Any]:
+        return self.header_values[item]
+
+    def getone(self, item):
+        # type: (str) -> T.Any
+        values = self[item]
+        if len(values) != 1:
+            raise ValueError("not one value for %r: %r" % (item, len(values)))
+        return values[0]
+
+    def subindex(self, filter_by_keys={}, **query):
+        # type: (T.Mapping[str, T.Any], T.Any) -> FileIndex
+        query.update(filter_by_keys)
+        raw_query = [(self.index_keys.index(k), v) for k, v in query.items()]
+        offsets = []
+        for header_values, offsets_values in self.offsets:
+            for idx, val in raw_query:
+                if header_values[idx] != val:
+                    break
+            else:
+                offsets.append((header_values, offsets_values))
+        index = type(self)(
+            filestream=self.filestream,
+            index_keys=self.index_keys,
+            offsets=offsets,
+            filter_by_keys=query,
+        )
+        return index
+
+    def first(self) -> Message:
+        with open(self.filestream.path, "rb") as file:
+            first_offset = self.offsets[0][1][0]
+            return self.filestream.message_from_file(file, offset=first_offset)