js

var year = 2015;
var month = 9;
var date = new Date(year, month-1);    /* js month begin with 0 */
var date_first = new Date(date.getFullYear(), date.getMonth(), 1);
var date_last = new Date(date.getFullYear(), date.getMonth() + 1, 0);

python

import datetime

cur_date_first = datetime.datetime(datetime.date
 
.today().year, datetime.date.today().month, 1)
cur_date_last = datetime.datetime(datetime.date.today().year, datetime.date.today().month+1, 1) - datetime.timedelta(1)

year = 2015
month = 8
date_first = datetime.datetime(year , month, 1)
date_last = datetime.datetime(year, month+1, 1) - datetime.timedelta
 
(1)

print date_first
print date_last