gistfile1.py

def crypto_aead_chacha20poly1305_encrypt(message,
                                         ad,
                                         nonce,
                                         key):

    mlen  = ctypes.c_ulonglong(len(message))
    adlen = ctypes.c_ulonglong(len(ad))

    c    =  ctypes.create_string_buffer(mlen.value+16L)
    clen  = ctypes.c_ulonglong(0)

    sodium.crypto_aead_chacha20poly1305_encrypt(c,
                                                clen,
                                                message,
                                                mlen,
                                                ad,
                                                adlen,
                                                None,
                                                nonce,
                                                key)
    return c.raw