Date Time convert Pandas

import datetime
    import calendar
    import pandas as pd
    #import snowflake.connector as sf

    filepath = 'MOODY_FILE.csv'
    id_vars = ["Mnemonic"," Concept"," Geography"," Description"," Last Updated", " Native Frequency", " Historical End Date"]

    df = pd.read_csv(filepath, delimiter=",")
    df1 = pd.melt(df, id_vars , var_name= 'PERIOD_END_DATE', value_name="MNEMONIC_VALUE")
    print(df1)
    vk=df1["PERIOD_END_DATE"]
    vkdate = pd.to_datetime(vk, format='%b-%y').date()
    ldays=calendar.monthrange(vkdate.year, vkdate.month)[-1]
    vkdate_new=datetime.date(int(vkdate.year), int(vkdate.month), int(ldays))
    print(vk)