137 lines
5.1 KiB
ReStructuredText
137 lines
5.1 KiB
ReStructuredText
Python 3 FAQ
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============
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.. contents::
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What Python 3 versions are supported?
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-------------------------------------
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PyMongo supports Python 3.x where x >= 2.
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Are there any PyMongo behavior changes with Python 3?
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-----------------------------------------------------
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Only one intentional change. Instances of :class:`bytes`
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are encoded as BSON type 5 (Binary data) with subtype 0.
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In Python 3 they are decoded back to :class:`bytes`. In
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Python 2 they will be decoded to :class:`~bson.binary.Binary`
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with subtype 0.
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For example, let's insert a :class:`bytes` instance using Python 3 then
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read it back. Notice the byte string is decoded back to :class:`bytes`::
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Python 3.2.5 (default, Feb 26 2014, 12:40:25)
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[GCC 4.7.3] on linux2
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pymongo
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>>> c = pymongo.MongoClient()
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>>> c.test.bintest.insert({'binary': b'this is a byte string'})
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ObjectId('4f9086b1fba5222021000000')
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>>> c.test.bintest.find_one()
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{'binary': b'this is a byte string', '_id': ObjectId('4f9086b1fba5222021000000')}
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Now retrieve the same document in Python 2. Notice the byte string is decoded
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to :class:`~bson.binary.Binary`::
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Python 2.7.6 (default, Feb 26 2014, 10:36:22)
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[GCC 4.7.3] on linux2
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pymongo
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>>> c = pymongo.MongoClient()
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>>> c.test.bintest.find_one()
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{u'binary': Binary('this is a byte string', 0), u'_id': ObjectId('4f9086b1fba5222021000000')}
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Why can't I share pickled ObjectIds between some versions of Python 2 and 3?
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----------------------------------------------------------------------------
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Instances of :class:`~bson.objectid.ObjectId` pickled using Python 2
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can always be unpickled using Python 3. Due to
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`http://bugs.python.org/issue13505 <http://bugs.python.org/issue13505>`_
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you must use Python 3.2.3 or newer to pickle instances of ObjectId if you
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need to unpickle them in Python 2.
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If you pickled an ObjectId using Python 2 and want to unpickle it using
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Python 3 you must pass ``encoding='latin-1'`` to pickle.loads::
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Python 2.7.6 (default, Feb 26 2014, 10:36:22)
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[GCC 4.7.3] on linux2
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pickle
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>>> from bson.objectid import ObjectId
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>>> oid = ObjectId()
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>>> oid
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ObjectId('4f919ba2fba5225b84000000')
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>>> pickle.dumps(oid)
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'ccopy_reg\n_reconstructor\np0\n(cbson.objectid\...'
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Python 3.2.5 (default, Feb 26 2014, 12:40:25)
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[GCC 4.7.3] on linux2
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pickle
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>>> pickle.loads(b'ccopy_reg\n_reconstructor\np0\n(cbson.objectid\...', encoding='latin-1')
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ObjectId('4f919ba2fba5225b84000000')
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If you need to pickle ObjectIds using Python 3 and unpickle them using Python 2
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you must use Python 3.2.3 or newer and ``protocol <= 2``::
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Python 3.2.3 (v3.2.3:3d0686d90f55, Apr 10 2012, 11:25:50)
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[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pickle
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>>> from bson.objectid import ObjectId
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>>> oid = ObjectId()
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>>> oid
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ObjectId('4f96f20c430ee6bd06000000')
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>>> pickle.dumps(oid, protocol=2)
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b'\x80\x02cbson.objectid\nObjectId\nq\x00)\x81q\x01c_codecs\nencode\...'
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Python 2.6.9 (unknown, Feb 26 2014, 12:39:10)
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[GCC 4.7.3] on linux2
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pickle
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>>> pickle.loads('\x80\x02cbson.objectid\nObjectId\nq\x00)\x81q\x01c_codecs\nencode\...')
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ObjectId('4f96f20c430ee6bd06000000')
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Unfortunately this won't work if you pickled the ObjectId using a Python 3
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version older than 3.2.3::
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Python 3.2.2 (default, Mar 21 2012, 14:32:23)
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[GCC 4.5.3] on linux2
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pickle
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>>> from bson.objectid import ObjectId
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>>> oid = ObjectId()
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>>> pickle.dumps(oid, protocol=2)
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b'\x80\x02cbson.objectid\nObjectId\nq\x00)\x81q\x01c__builtin__\nbytes\...'
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Python 2.4.6 (#1, Apr 12 2012, 14:48:24)
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[GCC 4.5.3] on linux3
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import pickle
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>>> pickle.loads('\x80\x02cbson.objectid\nObjectId\nq\x00)\x81q\x01c__builtin__\nbytes\...')
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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File "/usr/lib/python2.4/pickle.py", line 1394, in loads
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return Unpickler(file).load()
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File "/usr/lib/python2.4/pickle.py", line 872, in load
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dispatch[key](self)
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File "/usr/lib/python2.4/pickle.py", line 1104, in load_global
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klass = self.find_class(module, name)
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File "/usr/lib/python2.4/pickle.py", line 1140, in find_class
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klass = getattr(mod, name)
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AttributeError: 'module' object has no attribute 'bytes'
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.. warning::
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Unpickling in Python 2.6 or 2.7 an ObjectId pickled in a Python 3 version
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older than 3.2.3 will seem to succeed but the resulting ObjectId instance
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will contain garbage data.
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>>> pickle.loads('\x80\x02cbson.objectid\nObjectId\nq\x00)\x81q\x01c__builtin__\nbytes\...)
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ObjectId('5b37392c203135302c203234362c2034352c203235312c203136352c2033342c203532...')
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