如何使用 boto3 将 S3 对象保存到文件

Question

我正在尝试使用新的 boto3 AWS 客户端"hello world"。

我的用例非常简单：从 S3 获取对象并将其保存到文件中。

在 boto 2.X 我会这样做：

import boto
key = boto.connect_s3().get_bucket('foo').get_key('foo')
key.get_contents_to_filename('/tmp/foo')

在 boto 3 中。我找不到一种干净的方法来做同样的事情，所以我手动迭代 "Streaming" 对象：

import boto3
key = boto3.resource('s3').Object('fooo', 'docker/my-image.tar.gz').get()
with open('/tmp/my-image.tar.gz', 'w') as f:
    chunk = key['Body'].read(1024*8)
    while chunk:
        f.write(chunk)
        chunk = key['Body'].read(1024*8)

或

import boto3
key = boto3.resource('s3').Object('fooo', 'docker/my-image.tar.gz').get()
with open('/tmp/my-image.tar.gz', 'w') as f:
    for chunk in iter(lambda: key['Body'].read(4096), b''):
        f.write(chunk)

而且效果很好。我想知道是否有任何 "native" boto3 函数可以完成相同的任务？

Answer 1

最近 Boto3 中进行了自定义，这有助于解决这个问题（除其他外）。目前暴露在底层S3客户端，可以这样使用：

s3_client = boto3.client('s3')
open('hello.txt').write('Hello, world!')

# Upload the file to S3
s3_client.upload_file('hello.txt', 'MyBucket', 'hello-remote.txt')

# Download the file from S3
s3_client.download_file('MyBucket', 'hello-remote.txt', 'hello2.txt')
print(open('hello2.txt').read())

这些函数将自动处理 reading/writing 文件以及对大文件并行进行分段上传。

请注意，s3_client.download_file 不会创建目录。它可以创建为 pathlib.Path('/path/to/file.txt').parent.mkdir(parents=True, exist_ok=True).

Answer 2

boto3 现在有比客户端更好的界面：

resource = boto3.resource('s3')
my_bucket = resource.Bucket('MyBucket')
my_bucket.download_file(key, local_filename)

这本身并没有比接受的答案中的 client 好多少（尽管文档说它在失败时重试上传和下载做得更好）但考虑到资源通常更符合人体工程学（例如，s3 bucket and object 资源比客户端方法更好）这确实允许您留在资源层而不必下降。

Resources 通常可以用与客户端相同的方式创建，它们采用所有或大部分相同的参数，并将它们转发给它们的内部客户端。

Answer 3

想要模拟set_contents_from_string like boto2方法的小伙伴们，可以试试

import boto3
from cStringIO import StringIO

s3c = boto3.client('s3')
contents = 'My string to save to S3 object'
target_bucket = 'hello-world.by.vor'
target_file = 'data/hello.txt'
fake_handle = StringIO(contents)

# notice if you do fake_handle.read() it reads like a file handle
s3c.put_object(Bucket=target_bucket, Key=target_file, Body=fake_handle.read())

对于Python3:

在python3两者StringIO and cStringIO are gone。使用 StringIO 导入，如：

from io import StringIO

要同时支持两个版本：

try:
   from StringIO import StringIO
except ImportError:
   from io import StringIO

Answer 4

# Preface: File is json with contents: {'name': 'Android', 'status': 'ERROR'}

import boto3
import io

s3 = boto3.resource('s3')

obj = s3.Object('my-bucket', 'key-to-file.json')
data = io.BytesIO()
obj.download_fileobj(data)

# object is now a bytes string, Converting it to a dict:
new_dict = json.loads(data.getvalue().decode("utf-8"))

print(new_dict['status']) 
# Should print "Error"

Answer 5

注意：我假设您已经单独配置了身份验证。下面的代码是从 S3 存储桶下载单个对象。

import boto3

#initiate s3 client 
s3 = boto3.resource('s3')

#Download object to the file    
s3.Bucket('mybucket').download_file('hello.txt', '/tmp/hello.txt')

Answer 6

当您想读取一个配置与默认配置不同的文件时，可以直接使用 mpu.aws.s3_download(s3path, destination) 或复制粘贴代码：

def s3_download(source, destination,
                exists_strategy='raise',
                profile_name=None):
    """
    Copy a file from an S3 source to a local destination.

    Parameters
    ----------
    source : str
        Path starting with s3://, e.g. 's3://bucket-name/key/foo.bar'
    destination : str
    exists_strategy : {'raise', 'replace', 'abort'}
        What is done when the destination already exists?
    profile_name : str, optional
        AWS profile

    Raises
    ------
    botocore.exceptions.NoCredentialsError
        Botocore is not able to find your credentials. Either specify
        profile_name or add the environment variables AWS_ACCESS_KEY_ID,
        AWS_SECRET_ACCESS_KEY and AWS_SESSION_TOKEN.
        See https://boto3.readthedocs.io/en/latest/guide/configuration.html
    """
    exists_strategies = ['raise', 'replace', 'abort']
    if exists_strategy not in exists_strategies:
        raise ValueError('exists_strategy \'{}\' is not in {}'
                         .format(exists_strategy, exists_strategies))
    session = boto3.Session(profile_name=profile_name)
    s3 = session.resource('s3')
    bucket_name, key = _s3_path_split(source)
    if os.path.isfile(destination):
        if exists_strategy is 'raise':
            raise RuntimeError('File \'{}\' already exists.'
                               .format(destination))
        elif exists_strategy is 'abort':
            return
    s3.Bucket(bucket_name).download_file(key, destination)

from collections import namedtuple

S3Path = namedtuple("S3Path", ["bucket_name", "key"])


def _s3_path_split(s3_path):
    """
    Split an S3 path into bucket and key.

    Parameters
    ----------
    s3_path : str

    Returns
    -------
    splitted : (str, str)
        (bucket, key)

    Examples
    --------
    >>> _s3_path_split('s3://my-bucket/foo/bar.jpg')
    S3Path(bucket_name='my-bucket', key='foo/bar.jpg')
    """
    if not s3_path.startswith("s3://"):
        raise ValueError(
            "s3_path is expected to start with 's3://', " "but was {}"
            .format(s3_path)
        )
    bucket_key = s3_path[len("s3://"):]
    bucket_name, key = bucket_key.split("/", 1)
    return S3Path(bucket_name, key)

Answer 7

如果你想下载文件的一个版本，你需要使用get_object。

import boto3

bucket = 'bucketName'
prefix = 'path/to/file/'
filename = 'fileName.ext'

s3c = boto3.client('s3')
s3r = boto3.resource('s3')

if __name__ == '__main__':
    for version in s3r.Bucket(bucket).object_versions.filter(Prefix=prefix + filename):
        file = version.get()
        version_id = file.get('VersionId')
        obj = s3c.get_object(
            Bucket=bucket,
            Key=prefix + filename,
            VersionId=version_id,
        )
        with open(f"{filename}.{version_id}", 'wb') as f:
            for chunk in obj['Body'].iter_chunks(chunk_size=4096):
                f.write(chunk)

参考：https://botocore.amazonaws.com/v1/documentation/api/latest/reference/response.html

如何使用 boto3 将 S3 对象保存到文件

How to save S3 object to a file using boto3

python

amazon-web-services

boto

boto3