Python '；在<；字符串>'；需要字符串作为左操作数而不是列表

我的输入文件如下所示：

>seq_1
ATTAGACCTG
>seq_2
CCTGCCGGAA
>seq_3
AGACCTGCCG
>seq_4
GCCGGAATAC

我编写了以下代码以获得通用超弦：

from itertools import permutations

def parse_fasta (lines):
descs = []
seqs = []
data = ''
for line in lines:
    if line.startswith('>'):
        if data:
            seqs.append(data)
            data = ''
        descs.append(line)
    else:
        data += line.rstrip('\r\n')
seqs.append(data)
return descs, seqs

descriptions, sequences = parse_fasta(open('D:\python\input.fasta', 'r').read().split('\n'))

def solve(*strings):
"""
Given a list of strings, return the shortest string that contains them all.
"""
return min((simplify(p) for p in permutations(strings)), key=len)

def prefixes(s):
"""
Return a list of all the prefixes of the given string (including itself),
in ascending order (from shortest to longest).
"""
return [s[:i+1] for i in range(len(s))]
return [(i,s[:i+1]) for i in range(len(s))][::-1]

def simplify(strings):
"""
Given a list of strings, concatenate them wile removing overlaps between
successive elements.
"""
ret = ''
for s in strings:
    if s in ret:
        continue
    for i, prefix in reversed(list(enumerate(prefixes(s)))):
        if ret.endswith(prefix):
            ret += s[i+1:]
            break
    else:
        ret += s
return ret

print solve(sequences)  

我得到的错误如标题所示。当我给予

print solve('ATTAGACCTG','CCTGCCGGAA','AGACCTGCCG','GCCGGAATAC')

我得到了正确的输出。但是我想把我的输入作为程序中显示的文件。希望得到这样的结果：

ATTAGACCTGCCGGAATAC

---

请修复代码的标识。在

前缀中有两个连续返回。那不行。另外，你能解释一下你想要实现的算法吗？我删除了一个return语句，但仍然得到相同的错误解释一下算法，我会看一看。代码中给出了解释。