if datetime.strptime(item, '%Y') or datetime.strptime(item, '%b %d %y')  or datetime.strptime(item, '%b %d %Y')  or datetime.strptime(item, '%B %d %y')  or datetime.strptime(item, '%B %d %Y'):

if item is date:
    print date
else:
    print "Not a date"

from dateutil.parser import parse

def is_date(string):
    try:
        parse(string)
        return "is a date"
    except ValueError:
        return "not a date"

is_date("1990-12-1") # "is a date"
is_date("xyznotadate") # "not a date"

txt='''
Jan 19, 1990
January 19, 1990
Jan 19,1990
01/19/1990
01/19/90
1990
Jan 1990
January1990'''

import datetime as dt

fmts = ('%Y','%b %d, %Y','%b %d, %Y','%B %d, %Y','%B %d %Y','%m/%d/%Y','%m/%d/%y','%b %Y','%B%Y','%b %d,%Y')

parsed=[]
for e in txt.splitlines():
    for fmt in fmts:
        try:
           t = dt.datetime.strptime(e, fmt)
           parsed.append((e, fmt, t))
           break
        except ValueError as err:
           pass

# check that all the cases are handled
success={t[0] for t in parsed}
for e in txt.splitlines():
    if e not in success:
        print e

for t in parsed:
    print '"{:20}" => "{:20}" => {}'.format(*t)

"Jan 19, 1990        " => "%b %d, %Y           " => 1990-01-19 00:00:00
"January 19, 1990    " => "%B %d, %Y           " => 1990-01-19 00:00:00
"Jan 19,1990         " => "%b %d,%Y            " => 1990-01-19 00:00:00
"01/19/1990          " => "%m/%d/%Y            " => 1990-01-19 00:00:00
"01/19/90            " => "%m/%d/%y            " => 1990-01-19 00:00:00
"1990                " => "%Y                  " => 1990-01-01 00:00:00
"Jan 1990            " => "%b %Y               " => 1990-01-01 00:00:00
"January1990         " => "%B%Y                " => 1990-01-01 00:00:00