validation

str.capitalize(): returns a copy of the string with only its first character capitalized.

months = ['January',
          'February',
          'March',
          'April',
          'May',
          'June',
          'July',
          'August',
          'September',
          'October',
          'November',
          'December']
          
def valid_month(month):
    if month:
        cap_month = month.capitalize()
        if cap_month in months:
            return cap_month

use dictionary to restrict only three character.

month_abbvs = dic((m[:3].lower(), m) for m in months)
          
def valid_month(month):
    if month:
        short_month = month[:3].lower()
        return month_abbvs.get(short_month)

checking day

def valid_day(day):
    if day and day.isdigit():
     day = int(day)
     if day > 0 and <= 31:
         return day