If you are trying to take a value from the same array and trying to update it, you can use the following code.
{ 'condition': {
'ts': [ '5a81625ba0ff65023c729022',
'5a8161ada0ff65023c728f51',
'5a815fb4a0ff65023c728dcd']}
If the collection is userData['condition']['ts'] and we need to
for i,supplier in enumerate(userData['condition']['ts']):
supplier = ObjectId(supplier)
userData['condition']['ts'][i] = supplier
The output will be
{'condition': { 'ts': [ ObjectId('5a81625ba0ff65023c729022'),
ObjectId('5a8161ada0ff65023c728f51'),
ObjectId('5a815fb4a0ff65023c728dcd')]}