Add more dict-like interface to Tree

Signed-off-by: Cristian Le <cristian.le@mpsd.mpg.de>

Author: LecrisUT

fmf/base.py

@@ -58,7 +58,7 @@ def __init__(self, data: dict[str, Any] | str, name: str |
         """
 
         # Bail out if no data and no parent given
-        if not data and not parent:
+        if not data and parent is None:
             raise utils.GeneralError(
                 "No data or parent provided to initialize the tree.")
 
@@ -822,3 +822,18 @@ def __getitem__(self, key: str) -> Any:
             return self.children[key[1:]]
         else:
             return self.data[key]
+
+    def __len__(self) -> int:
+        return len(self.children) + len(self.data)
+
+    def __iter__(self) -> Iterator[Any]:
+        for c in self.children:
+            yield f"/{c}"
+        for d in self.data:
+            yield d
+
+    def __contains__(self, item: str):
+        if item.startswith("/"):
+            return item[1:] in self.children
+        else:
+            return item in self.data