'Creates an index on this collection.
Takes either a single key or a list of (key, direction) pairs.
The key(s) must be an instance of :class:`basestring`
(:class:`str` in python 3), and the direction(s) must be one of
(:data:`~pymongo.ASCENDING`, :data:`~pymongo.DESCENDING`,
:data:`~pymongo.GEO2D`, :data:`~pymongo.GEOHAYSTACK`,
:data:`~pymongo.GEOSPHERE`, :data:`~pymongo.HASHED`,
:data:`~pymongo.TEXT`).
To create a single key ascending index on the key ``\'mike\'`` we just
use a string argument::
>>> my_collection.create_index("mike")
For a compound index on ``\'mike\'`` descending and ``\'eliot\'``
ascending we need to use a list of tuples::
>>> my_collection.create_index([("mike", pymongo.DESCENDING),
...                             ("eliot", pymongo.ASCENDING)])
All optional index creation parameters should be passed as
keyword arguments to this method. For example::
>>> my_collection.create_index([("mike", pymongo.DESCENDING)],
...                            background=True)
Valid options include, but are not limited to:
- `name`: custom name to use for this index - if none is
given, a name will be generated.
- `unique`: if ``True`` creates a uniqueness constraint on the index.
- `background`: if ``True`` this index should be created in the
background.
- `sparse`: if ``True``, omit from the index any documents that lack
the indexed field.
- `bucketSize`: for use with geoHaystack indexes.
Number of documents to group together within a certain proximity
to a given longitude and latitude.
- `min`: minimum value for keys in a :data:`~pymongo.GEO2D`
index.
- `max`: maximum value for keys in a :data:`~pymongo.GEO2D`
index.
- `expireAfterSeconds`: <int> Used to create an expiring (TTL)
collection. MongoDB will automatically delete documents from
this collection after <int> seconds. The indexed field must
be a UTC datetime or the data will not expire.
- `partialFilterExpression`: A document that specifies a filter for
a partial index.
- `collation` (optional): An instance of
:class:`~pymongo.collation.Collation`. This option is only supported
on MongoDB 3.4 and above.
See the MongoDB documentation for a full list of supported options by
server version.
.. warning:: `dropDups` is not supported by MongoDB 3.0 or newer. The
option is silently ignored by the server and unique index builds
using the option will fail if a duplicate value is detected.
.. note:: `partialFilterExpression` requires server version **>= 3.2**
.. note:: The :attr:`~pymongo.collection.Collection.write_concern` of
this collection is automatically applied to this operation when using
MongoDB >= 3.4.
:Parameters:
- `keys`: a single key or a list of (key, direction)
pairs specifying the index to create
- `**kwargs` (optional): any additional index creation
options (see the above list) should be passed as keyword
arguments
.. versionchanged:: 3.4
Apply this collection\'s write concern automatically to this operation
when connected to MongoDB >= 3.4. Support the `collation` option.
.. versionchanged:: 3.2
Added partialFilterExpression to support partial indexes.
.. versionchanged:: 3.0
Renamed `key_or_list` to `keys`. Removed the `cache_for` option.
:meth:`create_index` no longer caches index names. Removed support
for the drop_dups and bucket_size aliases.
.. mongodoc:: indexes'

def create_index(self, keys, **kwargs):

    keys = helpers._index_list(keys)
    name = kwargs.setdefault('name', helpers._gen_index_name(keys))
    self.__create_index(keys, kwargs)
    return name
