ansible: make key_from_kwargs() 10x faster

It was half the cost of the service call

ansible_mitogen/services.py

@@ -38,6 +38,7 @@ when a child has completed a job.
 """
 
 from __future__ import absolute_import
+import hashlib
 import logging
 import os
 import os.path
@@ -114,11 +115,19 @@ class ContextService(mitogen.service.Service):
 
     def key_from_kwargs(self, **kwargs):
         """
-        Generate a deduplication key from the request. The default
-        implementation returns a string based on a stable representation of the
-        input dictionary generated by :py:func:`pprint.pformat`.
-        """
-        return pprint.pformat(kwargs)
+        Generate a deduplication key from the request.
+        """
+        out = []
+        stack = [kwargs]
+        while stack:
+            obj = stack.pop()
+            if isinstance(obj, dict):
+                stack.extend(sorted(obj.iteritems()))
+            elif isinstance(obj, (list, tuple)):
+                stack.extend(obj)
+            else:
+                out.append(str(obj))
+        return ''.join(out)
 
     def _produce_response(self, key, response):
         """