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.. contents::
What Python 3 versions are supported?
-------------------------------------
PyMongo supports CPython 3.4+ and PyPy3.
Are there any PyMongo behavior changes with Python 3?
-----------------------------------------------------
Only one intentional change. Instances of :class:`bytes`
are encoded as BSON type 5 (Binary data) with subtype 0.
In Python 3 they are decoded back to :class:`bytes`. In
Python 2 they are decoded to :class:`~bson.binary.Binary`
with subtype 0.
For example, let's insert a :class:`bytes` instance using Python 3 then
read it back. Notice the byte string is decoded back to :class:`bytes`::
Python 3.6.1 (v3.6.1:69c0db5050, Mar 21 2017, 01:21:04)
[GCC 4.9.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pymongo
>>> c = pymongo.MongoClient()
>>> c.test.bintest.insert_one({'binary': b'this is a byte string'}).inserted_id
ObjectId('4f9086b1fba5222021000000')
>>> c.test.bintest.find_one()
{'binary': b'this is a byte string', '_id': ObjectId('4f9086b1fba5222021000000')}
Now retrieve the same document in Python 2. Notice the byte string is decoded
to :class:`~bson.binary.Binary`::
Python 2.7.6 (default, Feb 26 2014, 10:36:22)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pymongo
>>> c = pymongo.MongoClient()
>>> c.test.bintest.find_one()
{u'binary': Binary('this is a byte string', 0), u'_id': ObjectId('4f9086b1fba5222021000000')}
There is a similar change in behavior in parsing JSON binary with subtype 0.
In Python 3 they are decoded into :class:`bytes`. In Python 2 they are
decoded to :class:`~bson.binary.Binary` with subtype 0.
For example, let's decode a JSON binary subtype 0 using Python 3. Notice the
byte string is decoded to :class:`bytes`::
Python 3.6.1 (v3.6.1:69c0db5050, Mar 21 2017, 01:21:04)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from bson.json_util import loads
>>> loads('{"b": {"$binary": "dGhpcyBpcyBhIGJ5dGUgc3RyaW5n", "$type": "00"}}')
{'b': b'this is a byte string'}
Now decode the same JSON in Python 2 . Notice the byte string is decoded
to :class:`~bson.binary.Binary`::
Python 2.7.10 (default, Feb 7 2017, 00:08:15)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from bson.json_util import loads
>>> loads('{"b": {"$binary": "dGhpcyBpcyBhIGJ5dGUgc3RyaW5n", "$type": "00"}}')
{u'b': Binary('this is a byte string', 0)}
Why can't I share pickled ObjectIds between some versions of Python 2 and 3?
----------------------------------------------------------------------------
Instances of :class:`~bson.objectid.ObjectId` pickled using Python 2
can always be unpickled using Python 3.
If you pickled an ObjectId using Python 2 and want to unpickle it using
Python 3 you must pass ``encoding='latin-1'`` to pickle.loads::
Python 2.7.6 (default, Feb 26 2014, 10:36:22)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> from bson.objectid import ObjectId
>>> oid = ObjectId()
>>> oid
ObjectId('4f919ba2fba5225b84000000')
>>> pickle.dumps(oid)
'ccopy_reg\n_reconstructor\np0\n(cbson.objectid\...'
Python 3.6.1 (v3.6.1:69c0db5050, Mar 21 2017, 01:21:04)
[GCC 4.9.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> pickle.loads(b'ccopy_reg\n_reconstructor\np0\n(cbson.objectid\...', encoding='latin-1')
ObjectId('4f919ba2fba5225b84000000')
If you need to pickle ObjectIds using Python 3 and unpickle them using Python 2
you must use ``protocol <= 2``::
Python 3.6.1 (v3.6.1:69c0db5050, Mar 21 2017, 01:21:04)
[GCC 4.9.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> from bson.objectid import ObjectId
>>> oid = ObjectId()
>>> oid
ObjectId('4f96f20c430ee6bd06000000')
>>> pickle.dumps(oid, protocol=2)
b'\x80\x02cbson.objectid\nObjectId\nq\x00)\x81q\x01c_codecs\nencode\...'
Python 2.6.9 (unknown, Feb 26 2014, 12:39:10)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> pickle.loads('\x80\x02cbson.objectid\nObjectId\nq\x00)\x81q\x01c_codecs\nencode\...')
ObjectId('4f96f20c430ee6bd06000000')
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