Unspecified syntax error

[hhydration]

def vigenere_encode(message, key):
    encoded= ''
    for c in range(len(message)):
        msg_char_index=alpha.index(message[c])
        key_char_index=alpha.index(key[(i% len(key))]
        enc_index=(msg_char_index + key_char_index)%(len(alpha))
        encoded += alpha[enc_index]]

Error:
 (user info), line 29
    enc_index=(msg_char_index + key_char_index)%(len(alpha))
    ^
SyntaxError: invalid syntax]

[ibreeden]

key_char_index=alpha.index(key[(i% len(key))]

It is the line before the error. A "close parenthesis" ")" is missing.