使用Python SDK从S3下载文件遇到空桶等运行错误求助

代码存在的核心问题 #

• 缩进逻辑错误：else: print('Bucket is empty')错误和下载判断逻辑对齐，本该对应obj_count > 0的判断分支，当桶内无对象时object_to_copy_index未定义会直接报错，桶内有对象时也会误触发空桶提示
• 下载返回值判断错误：boto3的s3.download_file方法执行成功返回None，你写的if s3_handle.download_file(...)判断永远为假，无法触发成功日志，逻辑完全错误
• 日志变量错误：日志里使用的obj["Key"]是遍历桶对象时的临时变量，最终只会指向最后一个遍历到的对象，不是你选中下载的文件
• 输入无校验：用户输入的索引如果不是合法数字、或者超出对象列表范围，直接转int会触发异常
• 无异常捕获：权限不足、网络故障、对象不存在等问题都会直接终止程序

修正后的代码 #

import logging
import botocore

# 提前配置logging，否则info日志不会输出
logging.basicConfig(level=logging.INFO)

def function_for_f(s3_handle=None):
    ## 列举存储桶并选择
    selected_bucket_name_origin = select_buckets(s3_handle=s3_handle)
    print(f"Selected bucket was: {selected_bucket_name_origin}")
    # 拉取桶内对象列表
    objects = list_bucket_objects_aws(s3_handle=s3_handle, bucket_name=selected_bucket_name_origin)
    
    if objects is None or len(objects) == 0:
        print('Bucket is empty')
        return
    
    # 打印可选对象列表
    for idx, obj in enumerate(objects):
        print(f'{idx}. {obj["Key"]}')
    
    # 校验用户输入
    while True:
        input_val = input('Which object to copy?')
        try:
            object_to_copy_index = int(input_val)
            if 0 <= object_to_copy_index < len(objects):
                break
            else:
                print(f"请输入0到{len(objects)-1}之间的数字")
        except ValueError:
            print("请输入合法的数字索引")
    
    selected_key = objects[object_to_copy_index]["Key"]
    print(f'Downloading {selected_key}')
    
    # 执行下载加异常捕获
    try:
        s3_handle.download_file(selected_bucket_name_origin, selected_key, '1.txt')
        logging.info(f'{selected_key} was downloaded from {selected_bucket_name_origin}')
    except botocore.exceptions.ClientError as e:
        if e.response['Error']['Code'] == "404":
            print("The object does not exist.")
        else:
            print(f"下载出错：{str(e)}")
            raise

内容的提问来源于stack exchange，提问作者Sergey V.