This is a function to check if a date string is in 'MMM DD YYYY' format, e.g. 'Oct 1 2012'.

check_date_format.py

def check_date_format(date):
    '''
    Check if that date string has a 'MMM DD YYYY' format. Return a boolean.
    '''
    output = True
    if isinstance(date,unicode) == False:
        return False
    month, day, year = date.split()
    if set(month) >= set(string.ascii_letters):
        return False
    if len(month) != 3:
        return False
    if set(day) >= set(string.digits):
        return False
    if len(day) not in [1,2]:
        return False
    if set(year) >= set(string.digits):
        return False
    if len(year) != 4:
        return False
    return output

First of all, it's not necessary to write isinstance(...) == False. For anything that returns a boolean result just use not, such as if not isinstance(...).
Second of all, datetime.strptime() :)