Count number of records in lmdb databse with python

I open a lmdb database using this code:

    lmdb_env = lmdb.open(source_path, readonly=True)

How can I count the number of records in this database?

I found a simple solution using for loop. Here it is:

count = 0
for key, value in lmdb_env.cursor():
        count = count + 1  

However, I think there should be a better way using pre-defined function.