提取fasta序列中的指定位置的长度序列的脚本

以下是一个 Python 脚本，可用于从 FASTA 格式的文件中提取指定位置的长度序列：

def read_fasta_file(filename):
    """读取 FASTA 格式的文件并返回一个字典，其中键为序列 ID，值为序列字符串"""
    sequences = {}
    with open(filename, 'r') as f:
        current_id = None
        current_sequence = ''
        for line in f:
            line = line.strip()
            if line.startswith('>'):
                if current_id is not None:
                    sequences[current_id] = current_sequence
                current_id = line[1:]
                current_sequence = ''
            else:
                current_sequence += line
        if current_id is not None:
            sequences[current_id] = current_sequence
    return sequences

def extract_sequence(sequence, start, end):
    """从序列中提取指定位置的长度序列"""
    return sequence[start-1:end]

if __name__ == '__main__':
    # 读取 FASTA 文件
    sequences = read_fasta_file('sequences.fasta')

    # 提取指定位置的长度序列
    sequence_id = 'sequence1'
    start = 10
    end = 20
    extracted_sequence = extract_sequence(sequences[sequence_id], start, end)

    # 输出结果
    print(f'>{sequence_id}_{start}_{end}')
    print(extracted_sequence)

你只需要将上述脚本中的 `sequences.fasta` 文件名、`sequence1` 序列 ID、`start` 和 `end` 位置替换为你自己的需要即可。