Added engine options to disable input/output data conversion

'yaql.convertInputData' and 'yaql.convertOutputData' engine
options were added.  By setting them to false one can suppress
input or output data conversion. For the input data this will prevent
yaql from converting mutable data structures (lists, dicts, sets) to
their immutable versions, which will break some of the constructs that
require hashable structures (for example set of lists, or list as a
dictionary key), for the output it will not expand produced iterators
and not convert tuples to lists. However this can greatly improve
performance in some cases

Change-Id: I240ce6646fe7dbc9522624739600b6c364bb9618

Author: Stan Lagun

yaql/__init__.py

@@ -67,7 +67,9 @@ def limit(iterator):
         @specs.inject('engine', yaqltypes.Engine())
         @specs.name('#finalize')
         def finalize(obj, limiter, engine):
-            return utils.convert_output_data(obj, limiter, engine)
+            if engine.options.get('yaql.convertOutputData', True):
+                return utils.convert_output_data(obj, limiter, engine)
+            return obj
 
         context.register_function(limit)
         context.register_function(finalize)

yaql/language/expressions.py

@@ -161,7 +161,10 @@ def evaluate(self, data=utils.NO_VALUE, context=None):
         if context is None or context is utils.NO_VALUE:
             context = yaql.create_context()
         if data is not utils.NO_VALUE:
-            context['$'] = utils.convert_input_data(data)
+            if self.engine.options.get('yaql.convertInputData', True):
+                context['$'] = utils.convert_input_data(data)
+            else:
+                context['$'] = data
         return self(utils.NO_VALUE, context, self.engine)
 
     def __str__(self):