concat or merge to data frame tables that do not have primary keys

I have 2 data frames

Generate single dataframe using 2 dataframe with different number of rows, combining the columns

we have 2 dataframes with different number of columns and rows. Want to combine both to a single dataframe in *python 3.7

Using pandas.concat along Axis 1 returns a Concatenation along Axis 0

I am trying to horizontally concatenate a pair of data frames with identical indices, but the result is always a vertical concatenation with NaN values inserted into every column.

How to concatenate two dataframes of one row each without generating NaN

I have two dataframes:

Concatenating two dataframes causes column header of index to disappear

I have two dataframes df_old and df_new.