def encode(arg):
    ''' Given that we're converting between variable formats,
        manual typechecking seems excusable here '''
    return {
        int : lambda x: 'i%ie' % x,
        str : lambda x: '%i:%s' % (len(x), x),
        list : lambda x: 'l%se' % ''.join(map(encode, arg)),
        dict : lambda x: 'd%se' % ''.join(''.join(map(encode, i)) for i in arg.items())
    }[type(arg)](arg)

def _eat_str(s):
    length,s = s.split(':', 1)
    length = int(length)
    return (s[:length], s[length:])

def _eat_int(s):
    val, s = s.split('e', 1)
    return int(val), s

def _eat_list(s):
    r = []
    while s[0] is not 'e':
        val, s = _eat_all(s)
        r.append(val)
    return r, s[1:]

def _eat_dict(s):
    r = {}
    while s[0] is not 'e':
        k,s = _eat_all(s)
        v,s = _eat_all(s)
        
        r[k] = v
    return r, s[1:]
    
def _eat_all(s):
    if s[0] in 'lid':
        val, s = {'l': _eat_list,
         'i': _eat_int,
         'd': _eat_dict}[s[0]](s[1:])
    else:
        val, s = _eat_str(s)
    if len(s):
        return (val, s)
    return val

def decode(s):
    try:
        val = _eat_all(s)
        if type(val) is tuple:
            #should NOT be a tuple, _eat_all would only return a list, dict,
            #or scalar
            raise ValueError, val[1]
        return val
    except ValueError, e:
        raise ValueError, 'Error somewhere in "%s"' % e