fix: Python 3 compatibility fixes

import reduce from functools

Undefined variable

erpnext/accounts/doctype/chart_of_accounts_importer/chart_of_accounts_importer.py

@@ -3,6 +3,7 @@
 # For license information, please see license.txt
 
 from __future__ import unicode_literals
+from functools import reduce
 import frappe, csv
 from frappe import _
 from frappe.utils import cstr

erpnext/regional/italy/utils.py

@@ -292,7 +292,7 @@ def prepare_and_attach_invoice(doc, replace=False):
 		"content": invoice_xml
 	})
 	_file.save()
-	return file
+	return _file
 
 @frappe.whitelist()
 def generate_single_invoice(docname):