Utils for streaming large files (S3, HDFS, gzip, bz2...)


smart_open -- utils for streaming large files

Travis License


smart_open is a Python 2 & Python 3 library for efficient streaming of very large files from/to S3, HDFS, WebHDFS or local (compressed) files. It is well tested (using moto), well documented and sports a simple, Pythonic API:

>>> # stream lines from an S3 object
>>> for line in smart_open.smart_open('s3://mybucket/mykey.txt'):
...    print line

>>> # using a completely custom s3 server, like s3proxy:
>>> for line in smart_open.smart_open('s3u://user:secret@host:port@mybucket/mykey.txt'):
...    print line

>>> # you can also use a boto.s3.key.Key instance directly:
>>> key = boto.connect_s3().get_bucket("my_bucket").get_key("my_key")
>>> with smart_open.smart_open(key) as fin:
...     for line in fin:
...         print line

>>> # can use context managers too:
>>> with smart_open.smart_open('s3://mybucket/mykey.txt') as fin:
...     for line in fin:
...         print line
...     fin.seek(0)  # seek to the beginning
...     print fin.read(1000)  # read 1000 bytes

>>> # stream from HDFS
>>> for line in smart_open.smart_open('hdfs://user/hadoop/my_file.txt'):
...     print line

>>> # stream from WebHDFS
>>> for line in smart_open.smart_open('webhdfs://host:port/user/hadoop/my_file.txt'):
...     print line

>>> # stream content *into* S3 (write mode):
>>> with smart_open.smart_open('s3://mybucket/mykey.txt', 'wb') as fout:
...     for line in ['first line', 'second line', 'third line']:
...          fout.write(line + '\n')

>>> # stream content *into* HDFS (write mode):
>>> with smart_open.smart_open('hdfs://host:port/user/hadoop/my_file.txt', 'wb') as fout:
...     for line in ['first line', 'second line', 'third line']:
...          fout.write(line + '\n')

>>> # stream content *into* WebHDFS (write mode):
>>> with smart_open.smart_open('webhdfs://host:port/user/hadoop/my_file.txt', 'wb') as fout:
...     for line in ['first line', 'second line', 'third line']:
...          fout.write(line + '\n')

>>> # stream from/to local compressed files:
>>> for line in smart_open.smart_open('./foo.txt.gz'):
...    print line

>>> for line in smart_open.smart_open('~/foo.txt.gz'):
...    print line

>>> with smart_open.smart_open('/home/radim/foo.txt.bz2', 'wb') as fout:
...    fout.write("some content\n")

Since going over all (or select) keys in an S3 bucket is a very common operation, there's also an extra method smart_open.s3_iter_bucket() that does this efficiently, processing the bucket keys in parallel (using multiprocessing):

>>> # get all JSON files under "mybucket/foo/"
>>> bucket = boto.connect_s3().get_bucket('mybucket')
>>> for key, content in s3_iter_bucket(bucket, prefix='foo/', accept_key=lambda key: key.endswith('.json')):
...     print key, len(content)

For more info (S3 credentials in URI, minimum S3 part size...) and full method signatures, check out the API docs:

>>> import smart_open
>>> help(smart_open.smart_open_lib)

S3-Specific Options

There are a few optional keyword arguments that are useful only for S3 access.

>>> smart_open.smart_open('s3://', host='s3.amazonaws.com')
>>> smart_open.smart_open('s3://', profile_name='my-profile')

These are both passed to boto.s3_connect() as keyword arguments. The S3 reader supports gzipped content, as long as the key is obviously a gzipped file (e.g. ends with ".gz").


Working with large S3 files using Amazon's default Python library, boto, is a pain. Its key.set_contents_from_string() and key.get_contents_as_string() methods only work for small files (loaded in RAM, no streaming). There are nasty hidden gotchas when using boto's multipart upload functionality, and a lot of boilerplate.

smart_open shields you from that. It builds on boto but offers a cleaner API. The result is less code for you to write and fewer bugs to make.


The module has no dependencies beyond Python >= 2.6 (or Python >= 3.3), boto and requests:

pip install smart_open

Or, if you prefer to install from the source tar.gz:

python setup.py test  # run unit tests
python setup.py install

To run the unit tests (optional), you'll also need to install mock , moto and responses <https://github.com/getsentry/responses> (pip install mock moto responses). The tests are also run automatically with Travis CI on every commit push & pull request.


smart_open is an ongoing effort. Suggestions, pull request and improvements welcome!

On the roadmap:

  • better documentation for the default file:// scheme

Comments, bug reports

smart_open lives on github. You can file issues or pull requests there.

smart_open is open source software released under the MIT license. Copyright (c) 2015-now Radim Řehůřek.