python - Get the duplicate value on DuplicateKeyError

Question

In pymongo, when a DuplicateKeyError caught, what's the proper way to find out the duplicate value behind the the exception?

Currently I do this

try:
    db.coll.insert({key: ['some_value', 'some_value_1']})
except pymongo.errors.DuplicateKeyError, e:
    dups = re.findall(r'{ +: +"(.*)" +}$', e.message)
    if len(dups) == 1:
        print dups[0]

It seems to work, but is there any easier way, like

try:
    db.coll.insert({key: ['some_value', 'some_value_1']})
except pymongo.errors.DuplicateKeyError, e:
    print e.dup_val

EDIT

It's a concurrent app, so check duplicates before insert might fail.

The field is an array, so it's hard to find out which one is the duplicate value.

Answer 1

In dev version of pymongo (2.7) you can check with error_document property:

try:
    db.coll.insert({name: 'some_value'})
except pymongo.errors.DuplicateKeyError, e:
    print e.error_document

As far as I know, in 2.6 and earlier versions, all info except error msg and code is discarded.