Obvio!!! read the code

Opción 1:

OpenERP localización mexico http://bazaar.launchpad.net/~openerp-mexico-maintainer/openerp-mexico-localization/trunk/files

Opción 2:

Factura Libre http://www.universolibre.org/node/6

Descarga la factura libre .. y ejecuta:

unzip FacturaLibreCFD22_RCX.oxt 

    zodman  $  unzip ../FacturaLibreCFD22_RC8.oxt 
    Archive:  ../FacturaLibreCFD22_RC8.oxt
    replace description.xml? [y]es, [n]o, [A]ll, [N]one, [r]ename: A
      inflating: description.xml         
      inflating: cfdi.py                 
      inflating: config~                 
      inflating: config.xcu              
      inflating: Addons.xcu              
      inflating: config.xcs              
      inflating: icons/preinvoice.png    
      inflating: icons/icon01.png        
      inflating: icons/productos_16.bmp  
      inflating: icons/logo.png          
      inflating: icons/filter.png        
      inflating: icons/config_16.bmp     
      inflating: icons/icon05.png        
      inflating: icons/regimen.png       
      inflating: icons/reinvoice.png     
      inflating: icons/cfd_16.bmp        
      inflating: icons/pdf.png           
      inflating: icons/ulm.png           
      inflating: icons/icon07.png        
      inflating: icons/icon02.png        
      inflating: icons/icon10.png        
      inflating: icons/admincfd_16.bmp   
      inflating: icons/clientes_16.bmp   
      inflating: icons/icon03.png        
      inflating: icons/note.png          
      inflating: icons/mail.png          
      inflating: icons/select.png        
      inflating: icons/icon06.png        
      inflating: icons/icon04.png        
      inflating: icons/entrar.png        
      inflating: icons/upload.png        
      inflating: icons/icon11.png        
      inflating: icons/product.png       
      inflating: icons/product-edit.png  
      inflating: icons/fields.png        
      inflating: icons/cancelar.png      
      inflating: icons/report.png        
      inflating: icons/xml.png           
      inflating: icons/pay.png           
      inflating: icons/icon08.png        
      inflating: icons/icon09.png        
      inflating: icons/product-delete.png  
      inflating: icons/sat.png           
      inflating: icons/salir.png         
      inflating: icons/product-add.png   
      inflating: icons/icon12.png        
      inflating: notices/notice.txt      
      inflating: bin/cadena22.xslt       
      inflating: bin/libeay32.dll        
      inflating: bin/plantilla_factura.ods  
      inflating: bin/pruebas.key         
      inflating: bin/ssleay32.dll        
      inflating: bin/zlib1.dll           
      inflating: bin/libxslt.dll         
      inflating: bin/iconv.dll           
      inflating: bin/pruebas.cer         
      inflating: bin/libxml2.dll         
      inflating: bin/xsltproc.exe        
      inflating: bin/openssl.exe         
      inflating: bin/libexslt.dll        
      inflating: dialogs/dlgConfig.xdl   
      inflating: dialogs/dlgNuevoProducto.xdl  
      inflating: dialogs/dlgProductosAdmin.xdl  
      inflating: dialogs/dlgRefacturar.xdl  
      inflating: dialogs/dlgRutas.xdl    
      inflating: dialogs/dlgClientes.xdl  
      inflating: dialogs/dlgReporteSAT.xdl  
      inflating: dialogs/dlgAdminCfdi.xdl  
      inflating: dialogs/dlgInput.xdl    
      inflating: dialogs/dlgCfdi.xdl     
      inflating: dialogs/dlgInput2.xdl   
      inflating: dialogs/dlgClientesAdmin.xdl  
      inflating: dialogs/dlgProductos.xdl  
      inflating: descriptions/desc.es    
      inflating: descriptions/desc.es~   
      inflating: pythonpath/pysqlite2/dbapi2.py  
      inflating: pythonpath/pysqlite2/dump.py  
      inflating: pythonpath/pysqlite2/__init__.py  
      inflating: pythonpath/pysqlite2/_sqlite.pyd  
      inflating: pythonpath/facturalibre/values.py  
      inflating: pythonpath/facturalibre/__init__.py  
      inflating: pythonpath/facturalibre/db/__init__.py  
      inflating: pythonpath/facturalibre/db/detalle.py  
      inflating: pythonpath/facturalibre/db/cp.sqlite  
      inflating: pythonpath/facturalibre/controllers/clientesadmin.py  
      inflating: pythonpath/facturalibre/controllers/admincfdi.py  
      inflating: pythonpath/facturalibre/controllers/cfdi.py  
      inflating: pythonpath/facturalibre/controllers/rutas.py  
      inflating: pythonpath/facturalibre/controllers/configuracion.py  
      inflating: pythonpath/facturalibre/controllers/__init__.py  
      inflating: pythonpath/facturalibre/controllers/reportesat.py  
      inflating: pythonpath/facturalibre/controllers/clientes.py  
      inflating: pythonpath/facturalibre/controllers/inputbox2.py  
      inflating: pythonpath/facturalibre/controllers/productosadmin.py  
      inflating: pythonpath/facturalibre/controllers/productos.py  
      inflating: pythonpath/facturalibre/controllers/inputbox.py  
      inflating: pythonpath/facturalibre/controllers/refacturar.py  
      inflating: pythonpath/facturalibre/ui/clientesadmin.py  
      inflating: pythonpath/facturalibre/ui/listenersadmin.py  
      inflating: pythonpath/facturalibre/ui/admincfdi.py  
      inflating: pythonpath/facturalibre/ui/cfdi.py  
      inflating: pythonpath/facturalibre/ui/rutas.py  
      inflating: pythonpath/facturalibre/ui/pyUnoGui.py  
      inflating: pythonpath/facturalibre/ui/configuracion.py  
      inflating: pythonpath/facturalibre/ui/listeners.py  
      inflating: pythonpath/facturalibre/ui/__init__.py  
      inflating: pythonpath/facturalibre/ui/reportesat.py  
      inflating: pythonpath/facturalibre/ui/clientes.py  
      inflating: pythonpath/facturalibre/ui/inputbox2.py  
      inflating: pythonpath/facturalibre/ui/productosadmin.py  
      inflating: pythonpath/facturalibre/ui/productos.py  
      inflating: pythonpath/facturalibre/ui/inputbox.py  
      inflating: pythonpath/facturalibre/ui/refacturar.py  
      inflating: pythonpath/facturalibre/modulos/pyUtil.py  
      inflating: pythonpath/facturalibre/modulos/pyPdf.py  
      inflating: pythonpath/facturalibre/modulos/__init__.py  
      inflating: pythonpath/facturalibre/modulos/pyXml.py  
      inflating: pythonpath/facturalibre/modulos/numlet.py  
      inflating: META-INF/manifest.xml   

Y veras todas las fuentes que estan en python usando pyuno.

Tryton hay te voy!