Inserting new attribute to a document using MongoDB ( Python )

You can update the document using $set.

http://www.mongodb.org/display/DOCS/Updating

Or you can get the document, edit it (using python code) and save it back.

To add to Taha's answer you can insert datetime attributes using currentDate:

db.getCollection("collection-name").update( 
{}, 
{
    $currentDate: {
        "date-field-name": { $type: "date" } // you can also use "timestamp" here
     }
}, 
false, true)

or to set a specific date you can use:

db.getCollection("collection-name").update( 
{}, 
{
    $set: {
        "date-field-name": ISODate("2020-01-23T04:05:06.007Z")
     }
}, 
false, true)

To insert a new attribute to all existing documents on a MongoDB collection, we can perform this method on our mongo shell:

db.collection.update( 
    {}, 
    {'$set': {"new_attribute":"attribute_value"}}, 
    false, 
    true
)

• {} it's the query criteria, in our case to add our new attribut to all our records, we pass an empty object {}
• {'$set': {"new_attribute":"attribute_value"}} means that using $set operator, insert on our records a new key "new_attribute" that will have this value "attribute_value"
• false it's upsert argument, it tells mongo to not insert a new document when no match is found
• true it's multi argument, it tells mongo to update multiple documents that meet the query criteria

To find more details check: https://docs.mongodb.com/manual/reference/method/db.collection.update/

db.collection.update({'_id' : ObjectId(...)}, 
                     {'$set' : {'create_time' : datetime(..) }})