Read multiple certificates from one file

multicert.py

import OpenSSL.crypto

def main():
    cert_file = '/Users/Simon/combined.pem'

    certificates = {}

    certificate_id = 0
    with open(cert_file, 'r') as f:
        for line in f:
            if "BEGIN" in line:
                certificate_id += 1

            certificates.setdefault(certificate_id, []).append(line)

    f.closed

    certificate_list = read_certificates(certificates)

    print "Got {} certificates from file".format(len(certificate_list))

    for cert in certificate_list:
        print cert.get_issuer()

def read_certificates(certs):
    certificate_list = []

    for k, lines in certs.iteritems():
        certificate_string = ''.join(lines)

        certificate = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_PEM, certificate_string)
        certificate_list.append(certificate)

    return certificate_list

if __name__ == "__main__":
    main()