[jmespath#186] options: add default not found value option

jmespath/visitor.py

@@ -1,8 +1,8 @@
 import operator
+from numbers import Number
 
 from jmespath import functions
 from jmespath.compat import string_type
-from numbers import Number
 
 
 def _equals(x, y):
@@ -58,7 +58,7 @@ def _is_actual_number(x):
 
 class Options(object):
  """Options to control how a JMESPath function is evaluated."""
- def __init__(self, dict_cls=None, custom_functions=None):
+ def __init__(self, dict_cls=None, custom_functions=None, not_found_value=None):
  #: The class to use when creating a dict. The interpreter
  # may create dictionaries during the evaluation of a JMESPath
  # expression. For example, a multi-select hash will
@@ -69,6 +69,7 @@ def __init__(self, dict_cls=None, custom_functions=None):
  # have predictable key ordering.
  self.dict_cls = dict_cls
  self.custom_functions = custom_functions
+ self.not_found_value = not_found_value
 
 
 class _Expression(object):
@@ -133,9 +134,9 @@ def visit_subexpression(self, node, value):
 
  def visit_field(self, node, value):
  try:
- return value.get(node['value'])
+ return value.get(node['value'], self._options.not_found_value)
  except AttributeError:
- return None
+ return self._options.not_found_value
 
  def visit_comparator(self, node, value):
  # Common case: comparator is == or !=
@@ -298,7 +299,7 @@ def _is_false(self, value):
  # because the truth/false values are different between
  # python and jmespath.
  return (value == '' or value == [] or value == {} or value is None or
- value is False)
+ value is False or value == self._options.not_found_value)
 
  def _is_true(self, value):
  return not self._is_false(value)

tests/test_search.py

@@ -62,3 +62,15 @@ def test_can_handle_decimals_as_numeric_type(self):
  result = decimal.Decimal('3')
  self.assertEqual(jmespath.search('[?a >= `1`].a', [{'a': result}]),
  [result])
+
+
+class TestNotFoundValueOption(unittest.TestCase):
+ opt = jmespath.Options(not_found_value='foo')
+
+ def test_can_supply_custom_not_found_value(self):
+ value = jmespath.search('b', {'a': 1}, self.opt)
+ self.assertEqual(value, 'foo')
+
+ def test_custom_value_is_treated_as_false(self):
+ value = jmespath.search('b || a', {'a': 1}, self.opt)
+ self.assertEqual(value, 1)