refactor: add type hints, remove comment, sort imports
diff --git a/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py b/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py
index 0d60173..9e5e63e 100644
--- a/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py
+++ b/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py
@@ -1,14 +1,28 @@
 # Copyright (c) 2013, Frappe Technologies Pvt. Ltd. and contributors
 # For license information, please see license.txt
 
+from collections import OrderedDict
+import datetime
+from typing import Dict, List, Tuple, Union
+
 import frappe
 from frappe import _
 from frappe.utils import date_diff
-from collections import OrderedDict
+
 from erpnext.accounts.report.general_ledger.general_ledger import get_gl_entries
 
 
-def execute(filters=None):
+Filters = frappe._dict
+Row = frappe._dict
+Data = List[Row]
+Columns = List[Dict[str, str]]
+DateTime = Union[datetime.date, datetime.datetime]
+FilteredEntries = List[Dict[str, Union[str, float, DateTime, None]]]
+ItemGroupsDict = Dict[Tuple[int, int], Dict[str, Union[str, int]]]
+SVDList = List[frappe._dict]
+
+
+def execute(filters: Filters) -> Tuple[Columns, Data]:
 	update_filters_with_account(filters)
 	validate_filters(filters)
 	columns = get_columns()
@@ -16,17 +30,17 @@
 	return columns, data
 
 
-def update_filters_with_account(filters):
+def update_filters_with_account(filters: Filters) -> None:
 	account = frappe.get_value("Company", filters.get("company"), "default_expense_account")
 	filters.update(dict(account=account))
 
 
-def validate_filters(filters):
+def validate_filters(filters: Filters) -> None:
 	if filters.from_date > filters.to_date:
 		frappe.throw(_("From Date must be before To Date"))
 
 
-def get_columns():
+def get_columns() -> Columns:
 	return [
 		{
 			'label': 'Item Group',
@@ -43,7 +57,7 @@
 	]
 
 
-def get_data(filters):
+def get_data(filters: Filters) -> Data:
 	filtered_entries = get_filtered_entries(filters)
 	svd_list = get_stock_value_difference_list(filtered_entries)
 	leveled_dict = get_leveled_dict()
@@ -62,7 +76,7 @@
 	return data
 
 
-def get_filtered_entries(filters):
+def get_filtered_entries(filters: Filters) -> FilteredEntries:
 	gl_entries = get_gl_entries(filters, [])
 	filtered_entries = []
 	for entry in gl_entries:
@@ -74,7 +88,7 @@
 	return filtered_entries
 
 
-def get_stock_value_difference_list(filtered_entries):
+def get_stock_value_difference_list(filtered_entries: FilteredEntries) -> SVDList:
 	voucher_nos = [fe.get('voucher_no') for fe in filtered_entries]
 	svd_list = frappe.get_list(
 		'Stock Ledger Entry', fields=['item_code','stock_value_difference'],
@@ -84,7 +98,7 @@
 	return svd_list
 
 
-def get_leveled_dict():
+def get_leveled_dict() -> OrderedDict:
 	item_groups_dict = get_item_groups_dict()
 	lr_list = sorted(item_groups_dict, key=lambda x : int(x[0]))
 	leveled_dict = OrderedDict()
@@ -109,14 +123,14 @@
 	return leveled_dict
 
 
-def assign_self_values(leveled_dict, svd_list):
+def assign_self_values(leveled_dict: OrderedDict, svd_list: SVDList) -> None:
 	key_dict = {v['name']:k for k, v in leveled_dict.items()}
 	for item in svd_list:
 		key = key_dict[item.get("item_group")]
 		leveled_dict[key]['self_value'] += -item.get("stock_value_difference")
 
 
-def assign_agg_values(leveled_dict):
+def assign_agg_values(leveled_dict: OrderedDict) -> None:
 	keys = list(leveled_dict.keys())[::-1]
 	prev_level = leveled_dict[keys[-1]]['level']
 	accu = [0]
@@ -141,21 +155,21 @@
 	leveled_dict[rk]['agg_value'] = sum(accu) + leveled_dict[rk]['self_value']
 
 
-def get_row(name:str, value:float, is_bold:int, indent:int):
+def get_row(name:str, value:float, is_bold:int, indent:int) -> Row:
 	item_group = name
 	if is_bold:
 		item_group = frappe.bold(item_group)
 	return frappe._dict(item_group=item_group, cogs_debit=value, indent=indent)
 			
 
-def assign_item_groups_to_svd_list(svd_list):
+def assign_item_groups_to_svd_list(svd_list: SVDList) -> None:
 	ig_map = get_item_groups_map(svd_list)
 	for item in svd_list:
 		item.item_group = ig_map[item.get("item_code")]
 
-def get_item_groups_map(svd_list):
-	# for items in svd_list: [{'item_code':'item_group'}]
-	item_codes = set([i['item_code'] for i in svd_list])
+
+def get_item_groups_map(svd_list: SVDList) -> Dict[str, str]:
+	item_codes = set(i['item_code'] for i in svd_list)
 	ig_list = frappe.get_list(
 		'Item', fields=['item_code','item_group'],
 		filters=[('item_code', 'in', item_codes)]
@@ -163,12 +177,12 @@
 	return {i['item_code']:i['item_group'] for i in ig_list}
 
 
-def get_item_groups_dict():
+def get_item_groups_dict() -> ItemGroupsDict:
 	item_groups_list = frappe.get_all("Item Group", fields=("name", "is_group", "lft", "rgt"))
 	return {(i['lft'],i['rgt']):{'name':i['name'], 'is_group':i['is_group']}
 		for i in item_groups_list}
 
 
-def update_leveled_dict(leveled_dict):
+def update_leveled_dict(leveled_dict: OrderedDict) -> None:
 	for k in leveled_dict:
 		leveled_dict[k].update({'self_value':0, 'agg_value':0})