I am trying to limit the BOMs that appear in a list based on products in a certain location, i have one function that executes sql to pull values from  the Bom and Bom_line tables to create a dictionary of related values. Then I compare this list with products in a location called WIP. and from that get a list of BOMs that should be available since their parts are available in the production environment. 

I have all of the code written my last step is to limit the BOM's that appear using a domain search for approved BOMS. my char value appears correctly. 

Code is below where enabled_boms appears as the char field correctly displaying [('id', '=', 9)]  in my app , which is correct, but appears as none.none when i print it in python. and then gives me Traceback:
Error: Expected attribute name, got (constant)

enabled_boms = fields.Char(compute='_compute_BOM_components')

print(enabled_boms)
BOM_production = fields.Many2one("mrp.bom", domain=enabled_boms)

I'm not sure how to get the returned value for enabled_boms to populate the domains section. 

my code runs if I hard code the

BOM_production = fields.Many2one('mrp.bom', domain = [('id', '=', 9)]) 

happy to share all of the code with whoever wants to take a look, just dont see value in posting it all here.