Hi,use attrs for the field in XML: defined create_uid in .py:

'create_uid': fields.many2one('res.users', 'Author', select=True, readonly=True),

the doc for create_uid link

• create_uid: user who created the record
• create_date: date when the record was created
• write_uid: last user who changed the record
• write_date: date of the last change to the record

Then in XML:

<field name="xxx" string=xxx" attrs="{'readonly':[('create_uid','!=',uid)]}"/>

But that the uid is currently not supported in the attrs attribute:

https://bugs.launchpad.net/openobject-server/+bug/920033

more details you may refer to:

Link

Hope it will help you!