def _subsequence(s, c):
    """
    Takes as parameter list like object s and returns the length of the longest 
    subsequence of s constituted only by consecutive character 'c's.
    Example: If the string passed as parameter is "001000111100", and c is '0',
    then the longest subsequence of only '0's has length 3.
    """
    bit = 0
    count = 0
    maxlen = 0
    for i in range(len(s)):
        bit = s[i]
        if bit == c:
            count = count + 1
            if count > maxlen:
                maxlen = count
        else:
            count = 0
    return maxlen
