S3Fs is a Pythonic file interface to S3. It builds on top of boto3.

The top-level class S3FileSystem holds connection information and allows typical file-system style operations like cp, mv, ls, du, glob, etc., as well as put/get of local files to/from S3.

The connection can be anonymous - in which case only publicly-available, read-only buckets are accessible - or via credentials explicitly supplied or in configuration files.

Calling open() on a S3FileSystem (typically using a context manager) provides an S3File for read or write access to a particular key. The object emulates the standard File protocol (read, write, tell, seek), such that functions expecting a file can access S3. Only binary read and write modes are implemented, with blocked caching.

This project was originally designed as a storage-layer interface for dask.distributed and has a very similar interface to hdfs3


Simple locate and read a file:

>>> import s3fs
>>> fs = s3fs.S3FileSystem(anon=True)
>>> fs.ls('my-bucket')
>>> with fs.open('my-bucket/my-file.txt', 'rb') as f:
...     print(f.read())
b'Hello, world'

(see also walk and glob)

Reading with delimited blocks:

>>> s3.read_block(path, offset=1000, length=10, delimiter=b'\n')
b'A whole line of text\n'

Writing with blocked caching:

>>> s3 = s3fs.S3FileSystem(anon=False)  # uses default credentials
>>> with s3.open('mybucket/new-file', 'wb') as f:
...     f.write(2*2**20 * b'a')
...     f.write(2*2**20 * b'a') # data is flushed and file closed
>>> s3.du('mybucket/new-file')
{'mybucket/new-file': 4194304}

Because S3Fs faithfully copies the Python file interface it can be used smoothly with other projects that consume the file interface like gzip or pandas.

>>> with s3.open('mybucket/my-file.csv.gz', 'rb') as f:
...     g = gzip.GzipFile(fileobj=f)  # Decompress data with gzip
...     df = pd.read_csv(g)           # Read CSV file with Pandas


This project is meant for convenience, rather than feature completeness. The following are known current omissions:

  • file access is always binary (although readline and iterating by line are


  • no permissions/access-control (i.e., no chmod/chmown methods)


The AWS key and secret may be provided explicitly when creating an S3FileSystem. A more secure way, not including the credentials directly in code, is to allow boto to establish the credentials automatically. Boto will try the following methods, in order:

  • aws_access_key_id, aws_secret_access_key, and aws_session_token environment


  • configuration files such as ~/.aws/credentials
  • for nodes on EC2, the IAM metadata provider

In a distributed environment, it is not expected that raw credentials should be passed between machines. In the explicitly provided credentials case, the method get_delegated_s3pars() can be used to obtain temporary credentials. When not using explicit credentials, it should be expected that every machine also has the appropriate environment variables, config files or IAM roles available.

If none of the credential methods are available, only anonymous access will work, and anon=True must be passed to the constructor.

Furthermore, S3FileSystem.current() will return the most-recently created instance, so this method could be used in preference to the constructor in cases where the code must be agnostic of the credentials/config used.

Requester Pays Buckets

Some buckets, such as the arXiv raw data, are configured so that the requester of the data pays any transfer fees. You must be authenticated to access these buckets and (because these charges maybe unexpected) amazon requires an additional key on many of the API calls. To enable RequesterPays create your file system as

>>> s3 = s3fs.S3FileSystem(anon=False, requester_pays=True)

Serverside Encryption

For some buckets/files you may want to use some of s3’s server side encryption features. s3fs supports these in a few ways

>>> s3 = s3fs.S3FileSystem(
...     s3_additional_kwargs={'ServerSideEncryption': 'AES256'})

This will create an s3 filesystem instance that will append the ServerSideEncryption argument to all s3 calls (where applicable).

The same applies for s3.open. Most of the methods on the filesystem object will also accept and forward keyword arguments to the underlying calls. The most recently specified argument is applied last in the case where both s3_additional_kwargs and a method’s **kwargs are used.

The s3.utils.SSEParams provides some convenient helpers for the serverside encryption parameters in particular. An instance can be passed instead of a regular python dictionary as the s3_additional_kwargs parameter.

Bucket Version Awareness

If your bucket has object versioning enabled then you can add version-aware support to s3fs. This ensures that if a file is opened at a particular point in time that version will be used for reading.

This mitigates the issue where more than one user is concurrently reading and writing to the same object.

s3 = s3fs.S3FileSytem(version_aware=True)

# Open the file at the latest version
fo = s3.open('versioned_bucket/object')

versions = s3.object_version_info('versioned_bucket/object')

# open the file at a particular version
fo_old_version = s3.open('versioned_bucket/object', version_id='SOMEVERSIONID')

In order for this to function the user must have the necessary IAM permissions to perform a GetObjectVersion

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