chore: remove all six compat code

erpnext/stock/utils.py

@@ -7,7 +7,6 @@ import json
 import frappe
 from frappe import _
 from frappe.utils import cstr, flt, get_link_to_form, nowdate, nowtime
-from six import string_types
 
 import erpnext
 
@@ -216,7 +215,7 @@ def update_bin(args, allow_negative_stock=False, via_landed_cost_voucher=False):
 def get_incoming_rate(args, raise_error_if_no_rate=True):
 	"""Get Incoming Rate based on valuation method"""
 	from erpnext.stock.stock_ledger import get_previous_sle, get_valuation_rate
-	if isinstance(args, string_types):
+	if isinstance(args, str):
 		args = json.loads(args)
 
 	in_rate = 0