Skip to main content

MessagePack (de)serializer.

Project description

MessagePack for Python

:author: INADA Naoki
:version: 0.4.0
:date: 2013-10-21

.. image::

What's this

`MessagePack <>`_ is a fast, compact binary serialization format, suitable for
similar data to JSON. This package provides CPython bindings for reading and
writing MessagePack data.

You can use ``pip`` or ``easy_install`` to install msgpack::

$ easy_install msgpack-python
$ pip install msgpack-python


msgpack-python provides pure python implementation.
PyPy can use this.


When you can't use binary distribution, you need to install Visual Studio
or Windows SDK on Windows. (NOTE: Visual C++ Express 2010 doesn't support
amd64. Windows SDK is recommanded way to build amd64 msgpack without any fee.)

Without extension, using pure python implementation on CPython runs slowly.


Note for msgpack 2.0 support

msgpack 2.0 adds two types: *bin* and *ext*.

*raw* was bytes or string type like Python 2's ``str``.
To distinguish string and bytes, msgpack 2.0 adds *bin*.
It is non-string binary like Python 3's ``bytes``.

To use *bin* type for packing ``bytes``, pass ``use_bin_type=True`` to
packer argument.

>>> import msgpack
>>> packed = msgpack.packb([b'spam', u'egg'], use_bin_type=True)
>>> msgpack.unpackb(packed, encoding='utf-8')
['spam', u'egg']

You shoud use it carefully. When you use ``use_bin_type=True``, packed
binary can be unpacked by unpackers supporting msgpack-2.0.

To use *ext* type, pass ``msgpack.ExtType`` object to packer.

>>> import msgpack
>>> packed = msgpack.packb(msgpack.ExtType(42, b'xyzzy'))
>>> msgpack.unpackb(packed)
ExtType(code=42, data='xyzzy')

You can use it with ``default`` and ``ext_hook``. See below.

Note for msgpack 0.2.x users

The msgpack 0.3 have some incompatible changes.

The default value of ``use_list`` keyword argument is ``True`` from 0.3.
You should pass the argument explicitly for backward compatibility.

`Unpacker.unpack()` and some unpack methods now raises `OutOfData`
instead of `StopIteration`.
`StopIteration` is used for iterator protocol only.

How to use

One-shot pack & unpack

Use ``packb`` for packing and ``unpackb`` for unpacking.
msgpack provides ``dumps`` and ``loads`` as alias for compatibility with
``json`` and ``pickle``.

``pack`` and ``dump`` packs to file-like object.
``unpack`` and ``load`` unpacks from file-like object.


>>> import msgpack
>>> msgpack.packb([1, 2, 3])
>>> msgpack.unpackb(_)
[1, 2, 3]

``unpack`` unpacks msgpack's array to Python's list, but can unpack to tuple::

>>> msgpack.unpackb(b'\x93\x01\x02\x03', use_list=False)
(1, 2, 3)

You should always pass the ``use_list`` keyword argument. See performance issues relating to use_list_ below.

Read the docstring for other options.

Streaming unpacking

``Unpacker`` is a "streaming unpacker". It unpacks multiple objects from one
stream (or from bytes provided through its ``feed`` method).


import msgpack
from io import BytesIO

buf = BytesIO()
for i in range(100):

unpacker = msgpack.Unpacker(buf)
for unpacked in unpacker:
print unpacked

Packing/unpacking of custom data type

It is also possible to pack/unpack custom data types. Here is an example for


import datetime

import msgpack

useful_dict = {
"id": 1,

def decode_datetime(obj):
if b'__datetime__' in obj:
obj = datetime.datetime.strptime(obj["as_str"], "%Y%m%dT%H:%M:%S.%f")
return obj

def encode_datetime(obj):
if isinstance(obj, datetime.datetime):
return {'__datetime__': True, 'as_str': obj.strftime("%Y%m%dT%H:%M:%S.%f")}
return obj

packed_dict = msgpack.packb(useful_dict, default=encode_datetime)
this_dict_again = msgpack.unpackb(packed_dict, object_hook=decode_datetime)

``Unpacker``'s ``object_hook`` callback receives a dict; the
``object_pairs_hook`` callback may instead be used to receive a list of
key-value pairs.

Extended types

It is also possible to pack/unpack custom data types using the msgpack 2.0 feature.

>>> import msgpack
>>> import array
>>> def default(obj):
... if isinstance(obj, array.array) and obj.typecode == 'd':
... return msgpack.ExtType(42, obj.tostring())
... raise TypeError("Unknown type: %r" % (obj,))
>>> def ext_hook(code, data):
... if code == 42:
... a = array.array('d')
... a.fromstring(data)
... return a
... return ExtType(code, data)
>>> data = array.array('d', [1.2, 3.4])
>>> packed = msgpack.packb(data, default=default)
>>> unpacked = msgpack.unpackb(packed, ext_hook=ext_hook)
>>> data == unpacked

Advanced unpacking control

As an alternative to iteration, ``Unpacker`` objects provide ``unpack``,
``skip``, ``read_array_header`` and ``read_map_header`` methods. The former two
read an entire message from the stream, respectively deserialising and returning
the result, or ignoring it. The latter two methods return the number of elements
in the upcoming container, so that each element in an array, or key-value pair
in a map, can be unpacked or skipped individually.

Each of these methods may optionally write the packed data it reads to a
callback function:


from io import BytesIO

def distribute(unpacker, get_worker):
nelems = unpacker.read_map_header()
for i in range(nelems):
# Select a worker for the given key
key = unpacker.unpack()
worker = get_worker(key)

# Send the value as a packed message to worker
bytestream = BytesIO()

Note about performance


CPython's GC starts when growing allocated object.
This means unpacking may cause useless GC.
You can use ``gc.disable()`` when unpacking large message.

`use_list` option
List is the default sequence type of Python.
But tuple is lighter than list.
You can use ``use_list=False`` while unpacking when performance is important.

Python's dict can't use list as key and MessagePack allows array for key of mapping.
``use_list=False`` allows unpacking such message.
Another way to unpacking such object is using ``object_pairs_hook``.

MessagePack uses `pytest` for testing.
Run test with following command:

$ py.test

vim: filetype=rst

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Files for msgpack-python, version 0.4.0
Filename, size File type Python version Upload date Hashes
Filename, size msgpack-python-0.4.0.tar.gz (111.4 kB) File type Source Python version None Upload date Hashes View

Supported by

AWS AWS Cloud computing Datadog Datadog Monitoring DigiCert DigiCert EV certificate Facebook / Instagram Facebook / Instagram PSF Sponsor Fastly Fastly CDN Google Google Object Storage and Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Salesforce Salesforce PSF Sponsor Sentry Sentry Error logging StatusPage StatusPage Status page