Python: merging two datasets via df.merge() is simply not working

I simply want to merg two datasets.

Sample df1:

Sample df2:

I want the result to look like this:

I always used to do it this way and it always worked:

df1.merge(df2, left_on=df1.index, right_on=df2.merge)

But now I am getting an error:
ValueError: Unable to fill values because RangeIndex cannot contain NA

These datasets have the same number of rows, so the indexes. Cannot understand what’s wrong. What do you think?

>Solution :

You can try pd.concat

df = pd.concat([df1, df2], axis=1)

Or with

df = df1.merge(df2, left_index=True, right_index=True)