import pymongo
from pymongo import MongoClient
import pandas as pd

def mongo_to_files(usr_name, pwd, address, db_name, collection,
                   out_path='out{}-{}.json', chunk_size=10000, port=27017):
    client = MongoClient(f'mongodb://{usr_name}:{pwd}@{address}', port)
    db = client[db_name]
    collection = db[collection]
    total = collection.count()
    n = 0
    while n < total:
        data = list(collection.find().skip(n).limit(chunk_size))
        for row in data:
            row.pop('_id')
        filename = out_path.format(n, n+chunk_size)
        pd.DataFrame(data).to_json(filename, orient='records', force_ascii=False)
        n += len(data)
    return n