When I used 2020+ to analyze example date, one error occurred at step 55

python `which 2020plus.py` --out-dir output_bladder/pretrained_output --log-level=INFO classify -n 200 --trained-classifier data/2020plus_10k.Rdata -d .7 -o 1.0 --features output_bladder/features.txt --null-distribution output_bladder/simulated_null_dist.txt --random-seed 71 --cv

Version: 1.2.3
Command: /home/ug0416/software/2020plus/2020plus.py --log-level=INFO classify --trained-classifier data/2020plus_10k.Rdata --null-distribution output_bladder/simulated_null_dist.txt --features output_bladder/simulated_summary/simulated_features.txt --simulated --cv
Running Random forest . . .
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AN ERROR HAS OCCURRED: check the log file
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Type: <class 'AttributeError'>

Exception: 'DataFrame' object has no attribute 'ix'

Traceback:
   File "/home/ug0416/software/2020plus/2020plus.py", line 275, in <module>
    args.func()  # run function corresponding to user's command
  File "/home/ug0416/software/2020plus/2020plus.py", line 37, in _classify
    src.classify.python.classifier.main(opts)  # run code
  File "/home/ug0416/software/2020plus/src/classify/python/classifier.py", line 190, in main
    result_df = trained_rand_forest_pred(rrclf, df, None, null_pvals, is_cv)
  File "/home/ug0416/software/2020plus/src/classify/python/classifier.py", line 104, in trained_rand_forest_pred
    onco_prob, tsg_prob, other_prob = clf.predict_cv()
  File "/home/ug0416/software/2020plus/src/classify/python/generic_classifier.py", line 136, in predict_cv
    test_feat = self.x.ix[new_genes]
  File "/home/ug0416/.local/lib/python3.6/site-packages/pandas/core/generic.py", line 5141, in __getattr__
    return object.__getattribute__(self, name)

R[write to console]: Warning message:

R[write to console]: package ‘randomForest’ was built under R version 4.0.3