File: README.rst

package info (click to toggle)
msgpack-python 0.4.2-1
  • links: PTS, VCS
  • area: main
  • in suites: jessie, jessie-kfreebsd
  • size: 964 kB
  • ctags: 1,594
  • sloc: cpp: 1,498; python: 1,434; makefile: 21
file content (259 lines) | stat: -rw-r--r-- 7,096 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
=======================
MessagePack for Python
=======================

:author: INADA Naoki
:version: 0.4.1
:date: 2014-02-17

.. image:: https://secure.travis-ci.org/msgpack/msgpack-python.png
   :target: https://travis-ci.org/#!/msgpack/msgpack-python

What's this
------------

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

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

   $ easy_install msgpack-python
     or
   $ pip install msgpack-python

PyPy
^^^^^

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

Windows
^^^^^^^

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.

Notes
-----

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])
   '\x93\x01\x02\x03'
   >>> 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):
      buf.write(msgpack.packb(range(i)))

   buf.seek(0)

   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
``datetime.datetime``.

::

    import datetime

    import msgpack

    useful_dict = {
        "id": 1,
        "created": datetime.datetime.now(),
    }

    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
    True


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()
            unpacker.skip(bytestream.write)
            worker.send(bytestream.getvalue())

Note about performance
------------------------

GC
^^

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``.


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

    $ py.test

..
    vim: filetype=rst