Upsert without specifying all parameters

I was hoping that I could just $set using "row" as it contains all the data I would want to update but get the following. My code is below:

c:\mongo scripts>csvimporter.py Traceback (most recent call last): .... pymongo.errors.WriteError: An empty update path is not valid.

def import_fame_dump(input_file='AB.csv'):
    fame_export = csv.DictReader(open(input_file), dialect='excel')
    leads = []

   fame_export.fieldnames + ['ImportDate']

for row in fame_export:
    row['ImportDate'] = datetime.datetime.utcnow()
    #leads.append(row)
    result = db.leads.update_one({
        'match1': row['match1'],
        'match2': row['match2'],
        'match3': row['match3'],
        'match4': row['match4']
        }, {"$set": row },
        upsert=True)

Many thanks for any assistance.