Answers for "join two dataframes pandas different date format"

pd combine date time

If df.Date and df.Time are of type str:
pd.to_datetime(df.Date + ' ' + df.Time)

If df.Date and df.Time are of type datetime.date and datetime.time respectively:
pd.to_datetime(df.Date.astype(str) + ' ' + df.Time.astype(str))

combining 2 dataframes pandas

df_3 = pd.concat([df_1, df_2])