queue_job: split identity_key hasher to ease reuse

You can now create your own identity exact matcher using the default hasher as a base.

queue_job/job.py

@@ -89,14 +89,19 @@ def identity_example(job_):
     Usually you will probably always want to include at least the name of the
     model and method.
     """
+    hasher = identity_exact_hasher(job_)
+    return hasher.hexdigest()
+
+
+def identity_exact_hasher(job_):
+    """Prepare hasher object for identity_exact."""
     hasher = hashlib.sha1()
     hasher.update(job_.model_name.encode("utf-8"))
     hasher.update(job_.method_name.encode("utf-8"))
     hasher.update(str(sorted(job_.recordset.ids)).encode("utf-8"))
     hasher.update(str(job_.args).encode("utf-8"))
     hasher.update(str(sorted(job_.kwargs.items())).encode("utf-8"))
-
-    return hasher.hexdigest()
+    return hasher
 
 
 @total_ordering