AttributeError append in DataFrame in validation_plots.ipynb

[wenzeslaus]

Our CI is partially failing. Likely, there was an incompatible update in a dependency which we did not pin. We need to fix the issue and possibly also pin the dependency version (or not).

Run jupyter nbconvert --execute --to notebook --inplace examples/notebooks/validation_plots.ipynb
[NbConvertApp] Converting notebook examples/notebooks/validation_plots.ipynb to notebook
Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.9.18/x64/bin/jupyter-nbconvert", line 8, in <module>
    sys.exit(main())
  File "/opt/hostedtoolcache/Python/3.9.18/x64/lib/python3.9/site-packages/jupyter_core/application.py", line 282, in launch_instance
    super().launch_instance(argv=argv, **kwargs)
...
  File "/opt/hostedtoolcache/Python/3.9.18/x64/lib/python3.9/site-packages/nbclient/client.py", line 914, in _check_raise_for_error
    raise CellExecutionError.from_cell_and_msg(cell, exec_reply_content)
nbclient.exceptions.CellExecutionError: An error occurred while executing the following cell:
------------------
# Combine dataframes from both tests to view contamination rates
contaminate_validation_df = contaminate_validation_df_1.append(contaminate_validation_df_2)
contaminate_validation_df.index = range(len(contaminate_validation_df))
------------------


---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
/tmp/ipykernel_1892/3158022213.py in ?()
----> 2 # Combine dataframes from both tests to view contamination rates
      3 contaminate_validation_df = contaminate_validation_df_1.append(contaminate_validation_df_2)
      4 contaminate_validation_df.index = range(len(contaminate_validation_df))

/opt/hostedtoolcache/Python/3.9.18/x64/lib/python3.9/site-packages/pandas/core/generic.py in ?(self, name)
   6200             and name not in self._accessors
   6201             and self._info_axis._can_hold_identifiers_and_holds_name(name)
   6202         ):
   6203             return self[name]
-> 6204         return object.__getattribute__(self, name)

AttributeError: 'DataFrame' object has no attribute 'append'