How to create collection with index if not exists in pymongo?

Question

I was using automatic collection creation in pymongo:

client = MongoClient(url)
db = client.get_default_database()
my_collection = db['my_collection']

I was thinking it created automatically on last statement and added

index_name = 'my_index'
if index_name not in my_collection.index_information():
     my_collection.create_index(..., name=index_name, unique=False)

Unfortunately, this led to error

pymongo.errors.OperationFailure: Collection ... doesn't exist

This made me think, that collection is created on first save. This gives me no place to put index creation code.

So, the question is: how to create collection with index, but only if it doesn't exist?

I have read this answer https://stackoverflow.com/a/9826294/258483 but don't like how it implies to write check of existence twice:

client = MongoClient(url)
db = client.get_default_database()
if 'my_collection' not in db.collection_names():
    db.createCollection('my_collection')

my_collection = db['my_collection']
index_name = 'my_index'
if index_name not in my_collection.index_information():
     my_collection.create_index(..., name=index_name, unique=False)   

Answer 1

As you see, calling index_information on a collection that doesn't exist yet throws OperationFailure.

Just call create_index without checking first:

client = MongoClient(url)
db = client.get_default_database()
my_collection = db['my_collection']
index_name = 'my_index'
my_collection.create_index(..., name=index_name, unique=False)

If the index already exists, the MongoDB server ignores the command. If the index does not exist, MongoDB creates the collection (if necessary) and the index on the collection.