Add dep

gammapy/modeling/fit.py

@@ -3,6 +3,8 @@
 import itertools
 import logging
 import collections.abc
+from abc import ABC
+
 import numpy as np
 from astropy.table import Table, QTable
 from gammapy.utils.pbar import progress_bar
@@ -899,7 +901,7 @@ def _repr_html_(self):
             return f"<pre>{html.escape(str(self))}</pre>"
 
 
-class FitResults(collections.abc.MutableSequence):
+class FitResults(collections.abc.MutableSequence, ABC):
     def __init__(self, results, axis_name=None):
         if np.array([not isinstance(result, FitResult) for result in results]).any():
             raise TypeError(f"Elements in {results!r} are not FitResult objects")