code: def unset_key(dotenv_path, key_to_unset, quote_mode="always"):
      
      if not os.path.exists(dotenv_path):
          warnings.warn("can't delete from %s - it doesn't exist." % dotenv_path)
          return None, key_to_unset
  
      removed = False
      with rewrite(dotenv_path) as (source, dest):
          for mapping in parse_stream(source):
              if mapping.key == key_to_unset:
                  removed = True
              else:
                  dest.write(mapping.original)
  
      if not removed:
          warnings.warn("key %s not removed from %s - key doesn't exist." % (key_to_unset, dotenv_path))
          return None, key_to_unset
  
      return removed, key_to_unset
docs: Removes a given key from the given .env
  
      If the .env path given doesn't exist, fails
      If the given key doesn't exist in the .env, fails