deribit: fill out docstr for `.api.get_values_from_cb_normalized_date()`

piker/brokers/deribit/api.py

@@ -1,5 +1,5 @@
 # piker: trading gear for hackers
-# Copyright (C) Guillermo Rodriguez (in stewardship for piker0)
+# Copyright (C) Guillermo Rodriguez (in stewardship for pikers)
 
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
@@ -80,7 +80,6 @@ from piker.accounting import (
 from piker.data import (
     def_iohlcv_fields,
     match_from_pairs,
-    # Struct,
 )
 from piker.data._web_bs import (
     open_jsonrpc_session
@@ -195,7 +194,11 @@ def cb_sym_to_deribit_inst(sym: Symbol) -> str:
 
 
 def get_values_from_cb_normalized_date(expiry_date: str) -> str:
-    # deribit specific
+    '''
+    Convert the `cryptofeed` (expiry) datetime format to our own,
+    a simple 3 token `str: f'{day}{month}{year}'.
+
+    '''
     cb_norm = [
         'F', 'G', 'H', 'J',
         'K', 'M', 'N', 'Q',