183 lines
7.1 KiB
ReStructuredText
183 lines
7.1 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 >= 1.
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We **do not** support Python 3.0.x. It has many problems
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(some that directly impact PyMongo) and was `end-of-lifed`_
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with the release of Python 3.1.
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.. _end-of-lifed: http://www.python.org/download/releases/3.0.1/
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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 3.1.4 (default, Mar 21 2012, 14:34:01)
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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 pymongo
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>>> c = pymongo.Connection()
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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 2.7.3 (default, Apr 12 2012, 10:35:17)
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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 pymongo
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>>> c = pymongo.Connection()
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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:`bytes` pickled in Python 3 versions older than 3.2.3
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can not be unpickled properly in Python 2. :class:`~bson.objectid.ObjectId`
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instances are implemented internally as packed binary data (:class:`str` in
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Python 2, :class:`bytes` in Python 3).
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Changes have been made to allow unpickling in Python 3 of instances
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pickled in Python 2. You just have to use the ``encoding`` parameter
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to pickle.loads::
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Python 2.7.3 (default, Apr 12 2012, 10:35:17)
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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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>>> 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 3.1.4 (default, Mar 21 2012, 14:34:01)
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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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>>> 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 pickled the ObjectId using Python 3.2.3 or newer you can unpickle the
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instance in Python 2. You just have to use ``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 2.4.4 (#1, Oct 18 2006, 10:34:39)
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[GCC 4.0.1 (Apple Computer, Inc. build 5341)] 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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>>> 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 in a Python 3 version
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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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See `http://bugs.python.org/issue13505 <http://bugs.python.org/issue13505>`_
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for more information about this issue.
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Why do I get a syntax error importing pymongo after installing from source?
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---------------------------------------------------------------------------
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PyMongo makes use of the 2to3 tool to translate much of its code to valid
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Python 3 syntax at install time. The translated modules are written to the
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build subdirectory before being installed, leaving the original source files
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intact. If you start the python interactive shell from the top level source
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directory after running ``python setup.py install`` the untranslated modules
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will be the first thing in your path. Importing pymongo will result in an
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exception similar to::
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Python 3.1.4 (default, Mar 21 2012, 14:34:01)
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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 pymongo
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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File "pymongo/__init__.py", line 104, in <module>
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from pymongo.connection import Connection
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File "pymongo/connection.py", line 573
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except Exception, why:
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^
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SyntaxError: invalid syntax
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Note the path in the traceback (``pymongo/__init__.py``). Changing out of the
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source directory takes the untranslated modules out of your path::
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$ cd ..
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$ python
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Python 3.1.4 (default, Mar 21 2012, 14:34:01)
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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 pymongo
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>>> pymongo.__file__
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'/home/behackett/py3k/lib/python3.1/site-packages/pymongo-2.2-py3.1-linux-x86_64.egg/pymongo/__init__.py'
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