向fasta文件中的标头添加序列长度

def add_sequence_length_to_fasta(fasta_file):
    # 打开fasta文件
    with open(fasta_file, 'r') as file:
        lines = file.readlines()

    modified_lines = []
    current_sequence = ""
    current_sequence_length = 0

    # 解析fasta文件
    for line in lines:
        if line.startswith(">"):  # 标头行
            # 添加序列长度信息
            if current_sequence:
                modified_lines.append(f">{current_sequence_length} {current_sequence}\n")
                current_sequence = ""
                current_sequence_length = 0

            # 提取标头信息
            header = line.strip()[1:]
            modified_lines.append(f">{header} ")
        else:  # 序列行
            sequence = line.strip()
            current_sequence += sequence
            current_sequence_length += len(sequence)

    # 添加最后一个序列的长度信息
    if current_sequence:
        modified_lines.append(f">{current_sequence_length} {current_sequence}\n")

    # 将修改后的内容写回fasta文件
    with open(fasta_file, 'w') as file:
        file.writelines(modified_lines)

# 使用示例
fasta_file = "example.fasta"
add_sequence_length_to_fasta(fasta_file)