Mongodb bulk write error

Ok, the problem was that i was assigning _id explicitly and it turns out that the string was larger than 12-byte limit, my bad.

It can be many reasons...
the best is that you try...catch... the exception and check in the errors

from pymongo.errors import BulkWriteError
try:
    bulk.execute()
except BulkWriteError as bwe:
    print(bwe.details)
    #you can also take this component and do more analysis
    #werrors = bwe.details['writeErrors']
    raise