mongo_client – Tools for connecting to MongoDB

Tools for connecting to MongoDB.

See also

High Availability and PyMongo for examples of connecting to replica sets or sets of mongos servers.

To get a Database instance from a MongoClient use either dictionary-style or attribute-style access:

>>> from pymongo import MongoClient
>>> c = MongoClient()
>>> c.test_database
Database(MongoClient('localhost', 27017), u'test_database')
>>> c['test-database']
Database(MongoClient('localhost', 27017), u'test-database')
class pymongo.mongo_client.MongoClient(host='localhost', port=27017, document_class=dict, tz_aware=False, connect=True, **kwargs)

Client for a MongoDB instance, a replica set, or a set of mongoses.

The client object is thread-safe and has connection-pooling built in. If an operation fails because of a network error, ConnectionFailure is raised and the client reconnects in the background. Application code should handle this exception (recognizing that the operation failed) and then continue to execute.

The host parameter can be a full mongodb URI, in addition to a simple hostname. It can also be a list of hostnames or URIs. Any port specified in the host string(s) will override the port parameter. If multiple mongodb URIs containing database or auth information are passed, the last database, username, and password present will be used. For username and passwords reserved characters like ‘:’, ‘/’, ‘+’ and ‘@’ must be escaped following RFC 2396.


When using PyMongo in a multiprocessing context, please read Using PyMongo with Multiprocessing first.

  • host (optional): hostname or IP address of the instance to connect to, or a mongodb URI, or a list of hostnames / mongodb URIs. If host is an IPv6 literal it must be enclosed in ‘[‘ and ‘]’ characters following the RFC2732 URL syntax (e.g. ‘[::1]’ for localhost)
  • port (optional): port number on which to connect
  • document_class (optional): default class to use for documents returned from queries on this client
  • tz_aware (optional): if True, datetime instances returned as values in a document by this MongoClient will be timezone aware (otherwise they will be naive)
  • connect (optional): if True (the default), immediately begin connecting to MongoDB in the background. Otherwise connect on the first operation.
Other optional parameters can be passed as keyword arguments:
  • maxPoolSize (optional): The maximum number of connections that the pool will open simultaneously. If this is set, operations will block if there are maxPoolSize outstanding connections from the pool. Defaults to 100. Cannot be 0.
  • socketTimeoutMS: (integer or None) Controls how long (in milliseconds) the driver will wait for a response after sending an ordinary (non-monitoring) database operation before concluding that a network error has occurred. Defaults to None (no timeout).
  • connectTimeoutMS: (integer or None) Controls how long (in milliseconds) the driver will wait during server monitoring when connecting a new socket to a server before concluding the server is unavailable. Defaults to 20000 (20 seconds).
  • serverSelectionTimeoutMS: (integer) Controls how long (in milliseconds) the driver will wait to find an available, appropriate server to carry out a database operation; while it is waiting, multiple server monitoring operations may be carried out, each controlled by connectTimeoutMS. Defaults to 30000 (30 seconds).
  • waitQueueTimeoutMS: (integer or None) How long (in milliseconds) a thread will wait for a socket from the pool if the pool has no free sockets. Defaults to None (no timeout).
  • waitQueueMultiple: (integer or None) Multiplied by maxPoolSize to give the number of threads allowed to wait for a socket at one time. Defaults to None (no limit).
  • socketKeepAlive: (boolean) Whether to send periodic keep-alive packets on connected sockets. Defaults to False (do not send keep-alive packets).
Write Concern options:
(Only set if passed. No default values.)
  • w: (integer or string) If this is a replica set, write operations will block until they have been replicated to the specified number or tagged set of servers. w=<int> always includes the replica set primary (e.g. w=3 means write to the primary and wait until replicated to two secondaries). Passing w=0 disables write acknowledgement and all other write concern options.
  • wtimeout: (integer) Used in conjunction with w. Specify a value in milliseconds to control how long to wait for write propagation to complete. If replication does not complete in the given timeframe, a timeout exception is raised.
  • j: If True block until write operations have been committed to the journal. Cannot be used in combination with fsync. Prior to MongoDB 2.6 this option was ignored if the server was running without journaling. Starting with MongoDB 2.6 write operations will fail with an exception if this option is used when the server is running without journaling.
  • fsync: If True and the server is running without journaling, blocks until the server has synced all data files to disk. If the server is running with journaling, this acts the same as the j option, blocking until write operations have been committed to the journal. Cannot be used in combination with j.
Replica set keyword arguments for connecting with a replica set - either directly or via a mongos:
  • replicaSet: (string or None) The name of the replica set to connect to. The driver will verify that all servers it connects to match this name. Implies that the hosts specified are a seed list and the driver should attempt to find all members of the set. Defaults to None.
  • read_preference: The read preference for this client. If connecting directly to a secondary then a read preference mode other than PRIMARY is required - otherwise all queries will throw AutoReconnect “not master”. See ReadPreference for all available read preference options. Defaults to PRIMARY.
SSL configuration:
  • ssl: If True, create the connection to the server using SSL. Defaults to False.
  • ssl_keyfile: The private keyfile used to identify the local connection against mongod. If included with the certfile then only the ssl_certfile is needed. Implies ssl=True. Defaults to None.
  • ssl_certfile: The certificate file used to identify the local connection against mongod. Implies ssl=True. Defaults to None.
  • ssl_cert_reqs: Specifies whether a certificate is required from the other side of the connection, and whether it will be validated if provided. It must be one of the three values ssl.CERT_NONE (certificates ignored), ssl.CERT_OPTIONAL (not required, but validated if provided), or ssl.CERT_REQUIRED (required and validated). If the value of this parameter is not ssl.CERT_NONE and a value is not provided for ssl_ca_certs PyMongo will attempt to load system provided CA certificates. If the python version in use does not support loading system CA certificates then the ssl_ca_certs parameter must point to a file of CA certificates. Implies ssl=True. Defaults to ssl.CERT_REQUIRED if not provided and ssl=True.
  • ssl_ca_certs: The ca_certs file contains a set of concatenated “certification authority” certificates, which are used to validate certificates passed from the other end of the connection. Implies ssl=True. Defaults to None.
  • ssl_match_hostname: If True (the default), and ssl_cert_reqs is not ssl.CERT_NONE, enables hostname verification using the match_hostname() function from python’s ssl module. Think very carefully before setting this to False as that could make your application vulnerable to man-in-the-middle attacks.

See also

See general MongoDB documentation


Changed in version 3.0: MongoClient is now the one and only client class for a standalone server, mongos, or replica set. It includes the functionality that had been split into MongoReplicaSetClient: it can connect to a replica set, discover all its members, and monitor the set for stepdowns, elections, and reconfigs.

The MongoClient constructor no longer blocks while connecting to the server or servers, and it no longer raises ConnectionFailure if they are unavailable, nor ConfigurationError if the user’s credentials are wrong. Instead, the constructor returns immediately and launches the connection process on background threads.

Therefore the alive method is removed since it no longer provides meaningful information; even if the client is disconnected, it may discover a server in time to fulfill the next operation.

In PyMongo 2.x, MongoClient accepted a list of standalone MongoDB servers and used the first it could connect to:

MongoClient(['', ''])

A list of multiple standalones is no longer supported; if multiple servers are listed they must be members of the same replica set, or mongoses in the same sharded cluster.

The behavior for a list of mongoses is changed from “high availability” to “load balancing”. Before, the client connected to the lowest-latency mongos in the list, and used it until a network error prompted it to re-evaluate all mongoses’ latencies and reconnect to one of them. In PyMongo 3, the client monitors its network latency to all the mongoses continuously, and distributes operations evenly among those with the lowest latency. See mongos Load Balancing for more information.

The connect option is added.

The start_request, in_request, and end_request methods are removed, as well as the auto_start_request option.

The copy_database method is removed, see the copy_database examples for alternatives.

The MongoClient.disconnect() method is removed; it was a synonym for close().

MongoClient no longer returns an instance of Database for attribute names with leading underscores. You must use dict-style lookups instead:




Disconnect from MongoDB.

Close all sockets in the connection pools and stop the monitor threads. If this instance is used again it will be automatically re-opened and the threads restarted.

c[db_name] || c.db_name

Get the db_name Database on MongoClient c.

Raises InvalidName if an invalid database name is used.


(host, port) of the current standalone, primary, or mongos, or None.

Accessing address raises InvalidOperation if the client is load-balancing among mongoses, since there is no single address. Use nodes instead.

New in version 3.0.


If this client if connected to a server that can accept writes.

True if the current server is a standalone, mongos, or the primary of a replica set.


If this client is connected to mongos.


The maximum number of sockets the pool will open concurrently.

When the pool has reached max_pool_size, operations block waiting for a socket to be returned to the pool. If waitQueueTimeoutMS is set, a blocked operation will raise ConnectionFailure after a timeout. By default waitQueueTimeoutMS is not set.


Set of all currently connected servers.


When connected to a replica set the value of nodes can change over time as MongoClient‘s view of the replica set changes. nodes can also be an empty set when MongoClient is first instantiated and hasn’t yet connected to any servers, or a network partition causes it to lose connection to all servers.


The largest BSON object the connected server accepts in bytes.

Defaults to 16MB if not connected to a server.


The largest message the connected server accepts in bytes.

Defaults to 32MB if not connected to a server.


The local threshold for this instance.


Read only access to the CodecOptions of this instance.


Read only access to the read preference of this instance.

Changed in version 3.0: The read_preference attribute is now read only.


Read only access to the WriteConcern of this instance.

Changed in version 3.0: The write_concern attribute is now read only.


Is this server locked? While locked, all write operations are blocked, although read operations may still be allowed. Use unlock() to unlock.


Get a list of the names of all databases on the connected server.


Drop a database.

Raises TypeError if name_or_database is not an instance of basestring (str in python 3) or Database.

  • name_or_database: the name of a database to drop, or a Database instance representing the database to drop

Get the database named in the MongoDB connection URI.

>>> uri = 'mongodb://host/my_database'
>>> client = MongoClient(uri)
>>> db = client.get_default_database()
>>> assert == 'my_database'

Useful in scripts where you want to choose which database to use based only on the URI in a configuration file.

get_database(name, codec_options=None, read_preference=None, write_concern=None)

Get a Database with the given name and options.

Useful for creating a Database with different codec options, read preference, and/or write concern from this MongoClient.

>>> client.read_preference
>>> db1 = client.test
>>> db1.read_preference
>>> from pymongo import ReadPreference
>>> db2 = client.get_database(
...     'test', read_preference=ReadPreference.SECONDARY)
>>> db2.read_preference

Get information about the MongoDB server we’re connected to.

close_cursor(cursor_id, address=None)

Close a single database cursor.

Raises TypeError if cursor_id is not an instance of (int, long). What closing the cursor actually means depends on this client’s cursor manager.

  • cursor_id: id of cursor to close
  • address (optional): (host, port) pair of the cursor’s server. If it is not provided, the client attempts to close the cursor on the primary or standalone, or a mongos server.

Changed in version 3.0: Added address parameter.

kill_cursors(cursor_ids, address=None)

Send a kill cursors message soon with the given ids.

Raises TypeError if cursor_ids is not an instance of list.

This method may be called from a Cursor destructor during garbage collection, so it isn’t safe to take a lock or do network I/O. Instead, we schedule the cursor to be closed soon on a background thread.

  • cursor_ids: list of cursor ids to kill
  • address (optional): (host, port) pair of the cursor’s server. If it is not provided, the client attempts to close the cursor on the primary or standalone, or a mongos server.

Changed in version 3.0: Now accepts an address argument. Schedules the cursors to be closed on a background thread instead of sending the message immediately.


Set this client’s cursor manager.

Raises TypeError if manager_class is not a subclass of CursorManager. A cursor manager handles closing cursors. Different managers can implement different policies in terms of when to actually kill a cursor that has been closed.

  • manager_class: cursor manager to use

Changed in version 3.0: Undeprecated.


Flush all pending writes to datafiles.


Optional parameters can be passed as keyword arguments:

  • lock: If True lock the server to disallow writes.
  • async: If True don’t block while synchronizing.


async and lock can not be used together.


MongoDB does not support the async option on Windows and will raise an exception on that platform.


Unlock a previously locked server.