OpenERP : Saving field value (amount) into an account
You can override "pay_and_reconcile" function to write in account field, this function is called at time of Pay.
action_date_assign()
action_move_create()
action_number()
this 3 function are called at time of validating invoice. 
You can override any one from this or you can add your own function . in workflow for the "open" activity.
I'm new to OpenERP and python and I need some help saving an amount into a particular account.
I have created a field in the invoice form that calculates a specific amount based on some code and displays that amount in the field. What I want to do is to associate an account with this field, so when the invoice is validated and/or payed, this amount is saved into an account and later on I can see it in the journal entries and/or chart of account. Any idea how to do that ?