Python 3 FAQ - PyMongo 4.13.2 documentation (original) (raw)
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What Python 3 versions are supported?¶
PyMongo supports CPython 3.9+ and PyPy3.10+.
Are there any PyMongo behavior changes with Python 3?¶
Only one intentional change. Instances of bytesare encoded as BSON type 5 (Binary data) with subtype 0. In Python 3 they are decoded back to bytes. In Python 2 they are decoded to Binarywith subtype 0.
For example, let’s insert a bytes instance using Python 3 then read it back. Notice the byte string is decoded back to bytes:
Python 3.7.9 (v3.7.9:13c94747c7, Aug 15 2020, 01:31:08) [Clang 6.0 (clang-600.0.57)] on darwin 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 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 bytes. In Python 2 they are decoded to Binary with subtype 0.
For example, let’s decode a JSON binary subtype 0 using Python 3. Notice the byte string is decoded to bytes:
Python 3.7.9 (v3.7.9:13c94747c7, Aug 15 2020, 01:31:08) [Clang 6.0 (clang-600.0.57)] 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 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 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 3.7.9 (v3.7.9:13c94747c7, Aug 15 2020, 01:31:08) [Clang 6.0 (clang-600.0.57)] on darwin 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 3.7.9 (v3.7.9:13c94747c7, Aug 15 2020, 01:31:08) [Clang 6.0 (clang-600.0.57)] on darwin 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 2.7.15 (default, Jun 21 2018, 15:00:48) [GCC 7.3.0] 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')