/usr/lib/python2.6/dist-packages/trytond/modules/purchase_invoice_line_standalone/purchase.py is in tryton-modules-purchase-invoice-line-standalone 2.2.0-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.6/dist-packages/trytond/modules/purchase_invoice_line_standalone/../../../../../../share/pyshared/trytond/modules/purchase_invoice_line_standalone/purchase.py