brotherton-erpnext/erpnext/patches/v11_0/move_leave_approvers_from_employee.py

import frappe
from frappe import _

def execute():
	frappe.reload_doc("hr", "doctype", "department_approver")
	frappe.reload_doc("hr", "doctype", "employee")
	frappe.reload_doc("hr", "doctype", "department")

	approvers = frappe.db.sql("""select distinct app.leave_approver, emp.department from
	`tabEmployee Leave Approver` app, `tabEmployee` emp
		where app.parenttype = 'Employee'
		and emp.name = app.parent
		""", as_dict=True)
	for record in approvers:
		if record.department:
			frappe.db.sql("""update `tabDepartment Approver` set parenttype = '{0}',
				parent = '{1}' and parentfield = 'leave_approver' where approver = '{2}'"""
				.format(_('Department'), record.department, record.leave_approver))