Thursday, September 04, 2014

SOLVED: MongoDB - Pymongo ConnectionFailure: function takes at most 4 arguments (5 given)

I was getting this odd message, leading to pymongo fail the Connection() and MongoClient() instantiation.  No connection?  Really?  Getting this message:

[user@boxnamehere:logs]$ python
Python 2.6.6 (r266:84292, Jul 20 2011, 10:22:43)
[GCC 4.4.5 20110214 (Red Hat 4.4.5-6)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from pymongo import MongoClient
>>> mc = MongoClient('servername.here', 11222)
Traceback (most recent call last):
  File "", line 1, in
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 369, in __init__
    raise ConnectionFailure(str(e))
pymongo.errors.ConnectionFailure: function takes at most 4 arguments (5 given)

So, what's wrong?  It's tough to find out.  I went in, backed-up and modified the files in the lib64/python2.6/site-packages/pymongo and bson/ dirs.  I imported traceback, added tb=format_exc() to each level of the try/except needed.  This gave me a really long traceback but at least I could see what was happening.

Once modified, my test program now produces:

user@boxname:~$ ./testPymongo.py
starting.
Traceback (most recent call last):
  File "./testPymongo.py", line 5, in
    mc = MC(host='servername.goes.here', port=11222, socketTimeoutMS=15000)
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 373, in __init__
    raise ConnectionFailure(msg)
pymongo.errors.ConnectionFailure: function takes at most 4 arguments (5 given) Traceback (most recent call last):
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 867, in __find_node
    member, nodes = self.__try_node(candidate)
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 714, in __try_node
    {'ismaster': 1})
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 695, in __simple_command
    response = helpers._unpack_response(response)['data'][0]
  File "/usr/lib64/python2.6/site-packages/pymongo/helpers.py", line 117, in _unpack_response
    compile_re)
TypeError: function takes at most 4 arguments (5 given)
, Traceback (most recent call last):
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 367, in __init__
    self._ensure_connected(True)
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 936, in _ensure_connected
    self.__ensure_member()
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 807, in __ensure_member
    member, nodes = self.__find_node()
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 900, in __find_node
    raise AutoReconnect(', '.join(errors))
AutoReconnect: function takes at most 4 arguments (5 given) Traceback (most recent call last):
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 867, in __find_node
    member, nodes = self.__try_node(candidate)
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 714, in __try_node
    {'ismaster': 1})
  File "/usr/lib64/python2.6/site-packages/pymongo/mongo_client.py", line 695, in __simple_command
    response = helpers._unpack_response(response)['data'][0]
  File "/usr/lib64/python2.6/site-packages/pymongo/helpers.py", line 117, in _unpack_response
    compile_re)
TypeError: function takes at most 4 arguments (5 given)

So, we see the problem is that the Pymongo version is calling, at about line 85 of /usr/lib64/python2.6/site-packages/pymongo/helpers.py

result["data"] = bson.decode_all(response[20:],
                                  as_class, tz_aware, uuid_subtype,
                                  compile_re)


But, when I go into /usr/lib64/python2.6/site-packages/bson/_init_.py I see function defined differently:

def decode_all(data, as_class=dict,
               tz_aware=True, uuid_subtype=OLD_UUID_SUBTYPE):
    """Decode BSON data to multiple documents.


So, I could fix this in the bson code, by adding an optional param.

Instead, though, I'm going to just remove the extraneous param since I'm thinking I don't need it.

Changeset: One file modified: /usr/lib64/python2.6/site-packages/pymongo/helpers.py

[user@server:pymongo]$ diff helpers.py helpers.py.orig
16,117c116,117
<                                      as_class, tz_aware, uuid_subtype
<                                     )
---
>                                      as_class, tz_aware, uuid_subtype,
>                                      compile_re)

*Solution*

Turns out, the problem isn't  with the code in pymongo.  It's that MongoDB Corp. has chosen to bundle their own version of the 'bson' package in with pymongo, and that version doesn't engage in happy-kindergarden-play with the pypy version of bson.

So, to fix this, do the following (omitting the $ prompts so you can cut and paste).  Note important steps of NOT BELIEVING PIP that it really uninstalled everything:


sudo pip uninstall bson
sudo pip uninstall pymongo
cd /usr/lib64/python2.6/site-packages
# Now, remove old versions of pymongo and bson.  Pip doesn't delete everything, dammit.
sudo rm -rf bson pymongo*
sudo pip install pymongo

Done!  Pymongo installs its own, proper version of bson.

Restart your processes and re-run your tests, it should work now.  Pymongo will connect to your mongo cluster properly, etc.

Note that the above problem occurs especially frequently if the box is under heavy load because (as we noted above) the initial connection raised an AutoReconnect. 

Enjoy your newfound powers in peace and with goodwill towards all.


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