Workflows can be moved along by sending them signals. Instead of using the top-level execute_kw, signals are sent using exec_workflow.
For example code is like below.

client = models.execute_kw(
    db, uid, password,
    'res.partner', 'search_read',
    [[('customer', '=', True)]],
    {'limit': 1, 'fields': [
        'property_account_receivable',
        'property_payment_term',
        'property_account_position']
    })[0]
invoice_id = models.execute_kw(
    db, uid, password,
    'account.invoice', 'create', [{
        'partner_id': client['id'],
        'account_id': client['property_account_receivable'][0],
        'invoice_line': [(0, False, {'name': "AAA"})]
    }])

models.exec_workflow(
    db, uid, password, 'account.invoice', 'invoice_open', invoice_id)

Note- Signals are sent to a specific record, and possibly trigger a transition on the workflow instance associated with the record.