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import requests
import datetime
def builtSession():
    email = "***"                                       
    passwd = "***"                                     
    loginurl = "https://rda.ucar.edu/cgi-bin/login"
    params = {"email":email, "password":passwd, "action":"login"}
    sess = requests.session()
    sess.post(loginurl,data=params)
    return sess
def download(sess, dt):
    g1 = datetime.datetime(1999,7,30,18)
    g2 = datetime.datetime(2007,12,6,12)
    if dt >= g2:
        suffix = "grib2"
    elif dt >= g1 and dt <g2:
        suffix = "grib1"
    else:
        raise StandardError("DateTime excess limit")
    url = "http://rda.ucar.edu/data/ds083.2"
    folder = "{}/{}/{}.{:0>2d}".format(suffix, dt.year, dt.year, dt.month)
    filename = "fnl_{}.{}".format(dt.strftime('%Y%m%d_%H_00'), suffix)
    fullurl = "/".join([url, folder, filename])
    r = sess.get(fullurl)
    with open(filename, "wb") as fw:
        fw.write(r.content)
    print(filename + " downloaded")
if __name__ == '__main__':
    print("downloading...")
    s = builtSession()
    for i in range(12):                                     
        startdt = datetime.datetime(2018, 5, 16, 0)  
        interval = datetime.interval(hours = i * 6)
        download(s,dt)
    print("download completed!")

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import os
import sys
import datetime
import urllib2
import cookielib

__all__ = ['fnl', 'gfs', 'era']


def fnl(dt, locapath):
    if not hasattr(dt, 'year'):
        return
    g1 = datetime.datetime(1999, 7, 30, 18)
    g2 = datetime.datetime(2007, 12, 6, 12)
    if dt >= g2:
        suffix = 'grib2'
    elif dt >= g1 and dt < g2:
        suffix = 'grib1'
    else:
        raise StandardError('DateTime excess limit')
    path = 'http://rda.ucar.edu/data/ds083.2'
    folder = '{}/{}/{}.{:0>2d}'.format(suffix, dt.year, dt.year, dt.month)
    filename = 'fnl_{}.{}'.format(dt.strftime('%Y%m%d_%H_00'), suffix)
    url = '/'.join([path, folder, filename])
    localfile = os.path.join(locapath, 'fnl', str(dt.year), filename)
    if os.path.exists(localfile):
        return
    print(url, localfile)
    urlopener = _loadcookie()
    _downloader(urlopener, url, localfile)
    return localfile


def gfs(dt, locapath):
    if not hasattr(dt, 'year'):
        return
    g1 = datetime.datetime(2006, 11, 1, 0)
    if dt < g1:
        raise StandardError('DateTime excess limit')
    else:
        suffix = 'grib2'
    path = 'http://rda.ucar.edu/data/ds335.0'
    folder = 'GFS0p5/{}'.format(dt.year)
    filename = 'GFS_Global_0p5deg_{}_anl.{}'.format(dt.strftime('%Y%m%d_%H00'), suffix)
    url = '/'.join([path, folder, filename])
    localfile = os.path.join(locapath, 'gfs', str(dt.year), filename)
    if os.path.exists(localfile):
        return
    print(url, localfile)
    urlopener = _loadcookie()
    _downloader(urlopener, url, localfile)
    return localfile

def _downloader(urlopener, url, localfile):
    sys.stdout.write('downloading {}...\n'.format(url))
    sys.stdout.flush()
    try:
        infile = urlopener.open(url)
        if not os.path.isdir(os.path.dirname(localfile)):
            os.makedirs(os.path.dirname(localfile))
        outfile = open(localfile, "wb")
        outfile.write(infile.read())
        outfile.close()
    except Exception as e:
        print(e)
        return
    sys.stdout.write('finish download {} and save it into {}\n'.format(url, localfile))
    sys.stdout.flush()


def _loadcookie(email='your email', passwd='your passwd'):
    cj = cookielib.MozillaCookieJar()
    opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(cj))
    do_authentication = False
    cj.load("auth.rda.ucar.edu", False, True)
    for cookie in cj:
        if (cookie.name == "sess" and cookie.is_expired()):
            do_authentication = True
    if (do_authentication):
        sys.stdout.write('Authentication start ...\n')
        sys.stdout.flush()
        opener.open('https://rda.ucar.edu/cgi-bin/login',
                    'email={}&password={}&action=login'.format(email, passwd))
        cj.clear_session_cookies()
        cj.save("auth.rda.ucar.edu", True, True)
        sys.stdout.write('Authentication finish and cookie has save into auth.rda.ucar.edu\n')
        sys.stdout.flush()
    return opener


if __name__ == '__main__':
    dt = datetime.datetime(2015, 10, 12, 00)
    fnl(dt, r'D:\FnlData')