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Description
Here is a sample code to reproduce the error:
In [1]: df1 = pd.DataFrame(np.random.rand(5,2))
df2 = pd.DataFrame(np.random.rand(5,2))
In [2]: df2.join(df1)
Out[2]: ---------------------------------------------------------------------------
ValueError: columns overlap but no suffix specified: RangeIndex(start=0, stop=2, step=1)
In [3]: df2.join(df1, lsuffix='_x', rsuffix='_x')
Out[2]: 0_x 1_x 0_x 1_x
0 0.904888 0.491802 0.509346 0.367847
1 0.282420 0.092652 0.672786 0.358450
2 0.339018 0.318990 0.359977 0.640366
3 0.775293 0.767872 0.820965 0.018728
4 0.543648 0.412799 0.650457 0.712789
So ultimately one does get a merged DataFrame with overlapping column names. Then why raise an error in the first place?
Note, I am using the latest Pandas, Python and Numpy.