Try this
new_df = pd.merge(A_df, B_df, how=’left’, left_on=[‘A_c1′,’c2’], right_on = [‘B_c1′,’c2′])
https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.merge.html
left_on : label or list, or array-like Field names to join on in left
DataFrame. Can be a vector or list of vectors of the length of the
DataFrame to use a particular vector as the join key instead of
columns
right_on : label or list, or array-like Field names to join on
in right DataFrame or vector/list of vectors per left_on docs
the problem here is that by using the apostrophes you are setting the value being passed to be a string, when in fact, as @Shijo stated from the documentation, the function is expecting a label or list, but not a string! If the list contains each of the name of the columns beings passed for both the left and right dataframe, then each column-name must individually be within apostrophes. With what has been stated, we can understand why this is inccorect:
new_df = pd.merge(A_df, B_df, how=’left’, left_on='[A_c1,c2]’, right_on = ‘[B_c1,c2]’)
And this is the correct way of using the function:
new_df = pd.merge(A_df, B_df, how=’left’, left_on=[‘A_c1′,’c2’], right_on = [‘B_c1′,’c2’])