Nothing links these data files except a positional index. You can execute the desired output result using pd.concat
pd.concat([distancesDF, datesDF.dates], axis=1)

To refer to edit comment and @kartik
if we create dfs to match what is displayed.
distances = {'names': ['A', 'B','C'] ,'distances':[100, 200, 300]} dates = {'flights': ['A', 'B', 'C'] ,'dates':['1/1/16', '1/2/16', '1/3/16']} distancesDF = pd.DataFrame(distances) datesDF = pd.DataFrame(dates)
then the following two parameters give the same and, possibly, the desired result.
mergers
distancesDF.merge(datesDF, left_on='names', right_on='flights')[['distances', 'names', 'dates']]
join to
distancesDF.join(datesDF.set_index('flights'), on='names')
both produce

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