import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-p', '--PDB', help='Enter PDB-ID in lower case. Eg: 1dgk', type=str)
options=parser.parse_args()

filename = 'pdb' + options.PDB + '.ent.gz'
import ftplib
ftp = ftplib.FTP('ftp.wwpdb.org')
ftp.login()
ftp.cwd('pub/pdb/data/structures/all/pdb')
file = open(filename, 'wb')
ftp.retrbinary('RETR ' + filename, file.write)
file.close()
ftp.quit()

print ('Check the script folder')