feat: add write_to_file as an attribute of written_key for easier access

dol/util.py

@@ -1909,9 +1909,9 @@ def written_key(
         If None, a temporary file is created.
         If a string starting with '*', the '*' is replaced with a unique temporary filename.
         If a string that has a '*' somewhere in the middle, what's on the left of if is used as a directory
-        and the '*' is replaced with a unique temporary filename. For example 
+        and the '*' is replaced with a unique temporary filename. For example
         '/tmp/*_file.ext' would be replaced with '/tmp/oiu8fj9873_file.ext'.
-        If a callable, it will be called with obj as input to get the key. One use case 
+        If a callable, it will be called with obj as input to get the key. One use case
         is to use a function that generates a key based on the object.
     :param obj_arg_position_in_writer: Position of the object argument in writer function (0 or 1).
 
@@ -2015,6 +2015,12 @@ def written_key(
     return key
 
 
+# Often, a user might want to encode an object before writing it to a file.
+# Therefore, they'll want to do a writer=Pipe(encoder, write_to_file), so we
+# put write_to_file as an attribute of written_key to have it handy.
+written_key.write_to_file = write_to_file
+
+
 # TODO: This function should be symmetric, and if so, the code should use recursion
 def invertible_maps(
     mapping: Mapping = None, inv_mapping: Mapping = None