diff --git a/stix2/base.py b/stix2/base.py
index 2afba16..7c62db4 100644
--- a/stix2/base.py
+++ b/stix2/base.py
@@ -185,7 +185,13 @@ class _STIXBase(collections.Mapping):
 
     # Handle attribute access just like key access
     def __getattr__(self, name):
-        if name in self:
+        # Pickle-proofing: pickle invokes this on uninitialized instances (i.e.
+        # __init__ has not run).  So no "self" attributes are set yet.  The
+        # usual behavior of this method reads an __init__-assigned attribute,
+        # which would cause infinite recursion.  So this check disables all
+        # attribute reads until the instance has been properly initialized.
+        unpickling = "_inner" not in self.__dict__
+        if not unpickling and name in self:
             return self.__getitem__(name)
         raise AttributeError("'%s' object has no attribute '%s'" %
                              (self.__class__.__name__, name))
@@ -236,6 +242,21 @@ class _STIXBase(collections.Mapping):
                 optional properties set to the default value defined in the spec.
             **kwargs: The arguments for a json.dumps() call.
 
+        Examples:
+            >>> import stix2
+            >>> identity = stix2.Identity(name='Example Corp.', identity_class='organization')
+            >>> print(identity.serialize(sort_keys=True))
+            {"created": "2018-06-08T19:03:54.066Z", ... "name": "Example Corp.", "type": "identity"}
+            >>> print(identity.serialize(sort_keys=True, indent=4))
+            {
+                "created": "2018-06-08T19:03:54.066Z",
+                "id": "identity--d7f3e25a-ba1c-447a-ab71-6434b092b05e",
+                "identity_class": "organization",
+                "modified": "2018-06-08T19:03:54.066Z",
+                "name": "Example Corp.",
+                "type": "identity"
+            }
+
         Returns:
             str: The serialized JSON object.
 
diff --git a/stix2/utils.py b/stix2/utils.py
index 619652a..137ea01 100644
--- a/stix2/utils.py
+++ b/stix2/utils.py
@@ -165,44 +165,87 @@ def _get_dict(data):
             raise ValueError("Cannot convert '%s' to dictionary." % str(data))
 
 
+def _iterate_over_values(dict_values, tuple_to_find):
+    """Loop recursively over dictionary values"""
+    from .base import _STIXBase
+    for pv in dict_values:
+        if isinstance(pv, list):
+            for item in pv:
+                if isinstance(item, _STIXBase):
+                    index = find_property_index(
+                        item,
+                        item.object_properties(),
+                        tuple_to_find
+                    )
+                    if index is not None:
+                        return index
+                elif isinstance(item, dict):
+                    for idx, val in enumerate(sorted(item)):
+                        if (tuple_to_find[0] == val and
+                                item.get(val) == tuple_to_find[1]):
+                            return idx
+        elif isinstance(pv, dict):
+            if pv.get(tuple_to_find[0]) is not None:
+                for idx, item in enumerate(sorted(pv.keys())):
+                    if ((item == tuple_to_find[0] and str.isdigit(item)) and
+                            (pv[item] == tuple_to_find[1])):
+                        return int(tuple_to_find[0])
+                    elif pv[item] == tuple_to_find[1]:
+                        return idx
+            for item in pv.values():
+                if isinstance(item, _STIXBase):
+                    index = find_property_index(
+                        item,
+                        item.object_properties(),
+                        tuple_to_find
+                    )
+                    if index is not None:
+                        return index
+                elif isinstance(item, dict):
+                    index = find_property_index(
+                        item,
+                        item.keys(),
+                        tuple_to_find
+                    )
+                    if index is not None:
+                        return index
+
+
 def find_property_index(obj, properties, tuple_to_find):
     """Recursively find the property in the object model, return the index
-    according to the _properties OrderedDict. If it's a list look for
-    individual objects. Returns and integer indicating its location
+    according to the ``properties`` OrderedDict when working with `stix2`
+    objects. If it's a list look for individual objects. Returns and integer
+    indicating its location.
+
+    Notes:
+        This method is intended to pretty print `stix2` properties for better
+        visual feedback when working with the library.
+
+    Warnings:
+        This method may not be able to produce the same output if called
+        multiple times and makes a best effort attempt to print the properties
+        according to the STIX technical specification.
+
+    See Also:
+        py:meth:`stix2.base._STIXBase.serialize` for more information.
+
     """
     from .base import _STIXBase
     try:
-        if tuple_to_find[1] in obj._inner.values():
-            return properties.index(tuple_to_find[0])
+        if isinstance(obj, _STIXBase):
+            if tuple_to_find[1] in obj._inner.values():
+                return properties.index(tuple_to_find[0])
+        elif isinstance(obj, dict):
+            for idx, val in enumerate(sorted(obj)):
+                if (tuple_to_find[0] == val and
+                        obj.get(val) == tuple_to_find[1]):
+                    return idx
         raise ValueError
     except ValueError:
-        for pv in obj._inner.values():
-            if isinstance(pv, list):
-                for item in pv:
-                    if isinstance(item, _STIXBase):
-                        val = find_property_index(item,
-                                                  item.object_properties(),
-                                                  tuple_to_find)
-                        if val is not None:
-                            return val
-                    elif isinstance(item, dict):
-                        for idx, val in enumerate(sorted(item)):
-                            if (tuple_to_find[0] == val and
-                                    item.get(val) == tuple_to_find[1]):
-                                return idx
-            elif isinstance(pv, dict):
-                if pv.get(tuple_to_find[0]) is not None:
-                    try:
-                        return int(tuple_to_find[0])
-                    except ValueError:
-                        return len(tuple_to_find[0])
-                for item in pv.values():
-                    if isinstance(item, _STIXBase):
-                        val = find_property_index(item,
-                                                  item.object_properties(),
-                                                  tuple_to_find)
-                        if val is not None:
-                            return val
+        if isinstance(obj, _STIXBase):
+            return _iterate_over_values(obj._inner.values(), tuple_to_find)
+        elif isinstance(obj, dict):
+            return _iterate_over_values(obj.values(), tuple_to_find)
 
 
 def new_version(data, **kwargs):

diff --git a/stix2/test/test_custom.py b/stix2/test/test_custom.py
index 7f91d79..6fb24d2 100644
--- a/stix2/test/test_custom.py
+++ b/stix2/test/test_custom.py
@@ -860,3 +860,33 @@ def test_register_custom_object():
 def test_extension_property_location():
     assert 'extensions' in stix2.v20.observables.OBJ_MAP_OBSERVABLE['x-new-observable']._properties
     assert 'extensions' not in stix2.v20.observables.EXT_MAP['domain-name']['x-new-ext']._properties
+
+
+@pytest.mark.parametrize("data", [
+    """{
+    "type": "x-example",
+    "id": "x-example--336d8a9f-91f1-46c5-b142-6441bb9f8b8d",
+    "created": "2018-06-12T16:20:58.059Z",
+    "modified": "2018-06-12T16:20:58.059Z",
+    "dictionary": {
+        "key": {
+            "key_a": "value",
+            "key_b": "value"
+        }
+    }
+}""",
+])
+def test_custom_object_nested_dictionary(data):
+    @stix2.sdo.CustomObject('x-example', [
+        ('dictionary', stix2.properties.DictionaryProperty()),
+    ])
+    class Example(object):
+        def __init__(self, **kwargs):
+            pass
+
+    example = Example(id='x-example--336d8a9f-91f1-46c5-b142-6441bb9f8b8d',
+                      created='2018-06-12T16:20:58.059Z',
+                      modified='2018-06-12T16:20:58.059Z',
+                      dictionary={'key': {'key_b': 'value', 'key_a': 'value'}})
+
+    assert data == str(example)
diff --git a/stix2/test/test_pickle.py b/stix2/test/test_pickle.py
new file mode 100644
index 0000000..9e2cc9a
--- /dev/null
+++ b/stix2/test/test_pickle.py
@@ -0,0 +1,17 @@
+import pickle
+
+import stix2
+
+
+def test_pickling():
+    """
+    Ensure a pickle/unpickle cycle works okay.
+    """
+    identity = stix2.Identity(
+        id="identity--d66cb89d-5228-4983-958c-fa84ef75c88c",
+        name="alice",
+        description="this is a pickle test",
+        identity_class="some_class"
+    )
+
+    pickle.loads(pickle.dumps(identity))
diff --git a/stix2/test/test_utils.py b/stix2/test/test_utils.py
index 655cd61..fb63ff7 100644
--- a/stix2/test/test_utils.py
+++ b/stix2/test/test_utils.py
@@ -1,3 +1,5 @@
+# -*- coding: utf-8 -*-
+
 import datetime as dt
 from io import StringIO
 
@@ -10,7 +12,7 @@ amsterdam = pytz.timezone('Europe/Amsterdam')
 eastern = pytz.timezone('US/Eastern')
 
 
-@pytest.mark.parametrize('dttm,timestamp', [
+@pytest.mark.parametrize('dttm, timestamp', [
     (dt.datetime(2017, 1, 1, tzinfo=pytz.utc), '2017-01-01T00:00:00Z'),
     (amsterdam.localize(dt.datetime(2017, 1, 1)), '2016-12-31T23:00:00Z'),
     (eastern.localize(dt.datetime(2017, 1, 1, 12, 34, 56)), '2017-01-01T17:34:56Z'),
@@ -76,12 +78,12 @@ def test_get_dict_invalid(data):
         stix2.utils._get_dict(data)
 
 
-@pytest.mark.parametrize('stix_id, typ', [
+@pytest.mark.parametrize('stix_id, type', [
     ('malware--d69c8146-ab35-4d50-8382-6fc80e641d43', 'malware'),
     ('intrusion-set--899ce53f-13a0-479b-a0e4-67d46e241542', 'intrusion-set')
 ])
-def test_get_type_from_id(stix_id, typ):
-    assert stix2.utils.get_type_from_id(stix_id) == typ
+def test_get_type_from_id(stix_id, type):
+    assert stix2.utils.get_type_from_id(stix_id) == type
 
 
 def test_deduplicate(stix_objs1):
@@ -100,3 +102,110 @@ def test_deduplicate(stix_objs1):
     assert "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f" in ids
     assert "2017-01-27T13:49:53.935Z" in mods
     assert "2017-01-27T13:49:53.936Z" in mods
+
+
+@pytest.mark.parametrize('object, tuple_to_find, expected_index', [
+    (stix2.ObservedData(
+        id="observed-data--b67d30ff-02ac-498a-92f9-32f845f448cf",
+        created_by_ref="identity--f431f809-377b-45e0-aa1c-6a4751cae5ff",
+        created="2016-04-06T19:58:16.000Z",
+        modified="2016-04-06T19:58:16.000Z",
+        first_observed="2015-12-21T19:00:00Z",
+        last_observed="2015-12-21T19:00:00Z",
+        number_observed=50,
+        objects={
+            "0": {
+                "name": "foo.exe",
+                "type": "file"
+            },
+            "1": {
+                "type": "ipv4-addr",
+                "value": "198.51.100.3"
+            },
+            "2": {
+                "type": "network-traffic",
+                "src_ref": "1",
+                "protocols": [
+                  "tcp",
+                  "http"
+                ],
+                "extensions": {
+                    "http-request-ext": {
+                        "request_method": "get",
+                        "request_value": "/download.html",
+                        "request_version": "http/1.1",
+                        "request_header": {
+                            "Accept-Encoding": "gzip,deflate",
+                            "User-Agent": "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.6) Gecko/20040113",
+                            "Host": "www.example.com"
+                        }
+                    }
+                }
+            }
+        },
+    ), ('1', {"type": "ipv4-addr", "value": "198.51.100.3"}), 1),
+    ({
+        "type": "x-example",
+        "id": "x-example--d5413db2-c26c-42e0-b0e0-ec800a310bfb",
+        "created": "2018-06-11T01:25:22.063Z",
+        "modified": "2018-06-11T01:25:22.063Z",
+        "dictionary": {
+            "key": {
+                "key_one": "value",
+                "key_two": "value"
+            }
+        }
+    }, ('key', {'key_one': 'value', 'key_two': 'value'}), 0),
+    ({
+        "type": "language-content",
+        "id": "language-content--b86bd89f-98bb-4fa9-8cb2-9ad421da981d",
+        "created": "2017-02-08T21:31:22.007Z",
+        "modified": "2017-02-08T21:31:22.007Z",
+        "object_ref": "campaign--12a111f0-b824-4baf-a224-83b80237a094",
+        "object_modified": "2017-02-08T21:31:22.007Z",
+        "contents": {
+            "de": {
+                "name": "Bank Angriff 1",
+                "description": "Weitere Informationen über Banküberfall"
+            },
+            "fr": {
+                "name": "Attaque Bank 1",
+                "description": "Plus d'informations sur la crise bancaire"
+            }
+        }
+    }, ('fr', {"name": "Attaque Bank 1", "description": "Plus d'informations sur la crise bancaire"}), 1)
+])
+def test_find_property_index(object, tuple_to_find, expected_index):
+    assert stix2.utils.find_property_index(
+        object,
+        [],
+        tuple_to_find
+    ) == expected_index
+
+
+@pytest.mark.parametrize('dict_value, tuple_to_find, expected_index', [
+    ({
+        "contents": {
+            "de": {
+                "name": "Bank Angriff 1",
+                "description": "Weitere Informationen über Banküberfall"
+            },
+            "fr": {
+                "name": "Attaque Bank 1",
+                "description": "Plus d'informations sur la crise bancaire"
+            },
+            "es": {
+                "name": "Ataque al Banco",
+                "description": "Mas informacion sobre el ataque al banco"
+            }
+        }
+    }, ('es', {"name": "Ataque al Banco", "description": "Mas informacion sobre el ataque al banco"}), 1),  # Sorted alphabetically
+    ({
+        'my_list': [
+            {"key_one": 1},
+            {"key_two": 2}
+        ]
+    }, ('key_one', 1), 0)
+])
+def test_iterate_over_values(dict_value, tuple_to_find, expected_index):
+    assert stix2.utils._iterate_over_values(dict_value.values(), tuple_to_find) == expected_index

Custom STIX objects with nested dictionary error
A custom STIX object with a nested dictionary created using the following example:

``` python
#!/usr/bin/env python3.6

from stix2 import CustomObject, properties

@CustomObject('x-example', [
    ('dictionary', properties.DictionaryProperty()),
])
class Example(object):
    def __init__(self, **kwargs):
        pass

example = Example(dictionary={'key':{'key_one':'value', 'key_two':'value'}})

print(example)
```

throws the following error when calling the `__str__()` method:

``` bash
Traceback (most recent call last):
  File "./example.py", line 16, in <module>
    print(example)
  File "/home/lib64/python3.6/site-packages/stix2/base.py", line 199, in __str__
    return self.serialize(pretty=True)
  File "/home/lib64/python3.6/site-packages/stix2/base.py", line 262, in serialize
    return json.dumps(self, cls=STIXJSONEncoder, **kwargs)
  File "/home/lib64/python3.6/site-packages/simplejson/__init__.py", line 399, in dumps
    **kw).encode(obj)
  File "home/lib64/python3.6/site-packages/simplejson/encoder.py", line 298, in encode
    chunks = list(chunks)
  File "/home/lib64/python3.6/site-packages/simplejson/encoder.py", line 717, in _iterencode
    for chunk in _iterencode(o, _current_indent_level):
  File "home/lib64/python3.6/site-packages/simplejson/encoder.py", line 696, in _iterencode
    for chunk in _iterencode_dict(o, _current_indent_level):
  File "home/lib64/python3.6/site-packages/simplejson/encoder.py", line 652, in _iterencode_dict
    for chunk in chunks:
  File "/home/lib64/python3.6/site-packages/simplejson/encoder.py", line 652, in _iterencode_dict
    for chunk in chunks:
  File "/home/lib64/python3.6/site-packages/simplejson/encoder.py", line 602, in _iterencode_dict
    items.sort(key=_item_sort_key)
TypeError: '<' not supported between instances of 'NoneType' and 'NoneType'
```

the work around is to call:

``` python
print(example.serialize(pretty=False))
```

I'm assuming its something do with how `simplejson` is trying to sort the keys and struggles with the nested dictionary. Is there a reason why the `__str__()` method defaults to `pretty=True`?
stix2/test/test_custom.py::test_custom_object_nested_dictionary[{\n stix2/test/test_pickle.py::test_pickling stix2/test/test_utils.py::test_find_property_index[object1-tuple_to_find1-0] stix2/test/test_utils.py::test_find_property_index[object2-tuple_to_find2-1] stix2/test/test_utils.py::test_iterate_over_values[dict_value0-tuple_to_find0-1] stix2/test/test_utils.py::test_iterate_over_values[dict_value1-tuple_to_find1-0]
stix2/test/test_custom.py::test_identity_custom_property stix2/test/test_custom.py::test_identity_custom_property_invalid stix2/test/test_custom.py::test_identity_custom_property_allowed stix2/test/test_custom.py::test_parse_identity_custom_property[{\n stix2/test/test_custom.py::test_custom_property_object_in_bundled_object stix2/test/test_custom.py::test_custom_properties_object_in_bundled_object stix2/test/test_custom.py::test_custom_property_dict_in_bundled_object stix2/test/test_custom.py::test_custom_properties_dict_in_bundled_object stix2/test/test_custom.py::test_custom_property_in_observed_data stix2/test/test_custom.py::test_custom_property_object_in_observable_extension stix2/test/test_custom.py::test_custom_property_dict_in_observable_extension stix2/test/test_custom.py::test_identity_custom_property_revoke stix2/test/test_custom.py::test_identity_custom_property_edit_markings stix2/test/test_custom.py::test_custom_object_raises_exception stix2/test/test_custom.py::test_custom_object_type stix2/test/test_custom.py::test_custom_object_invalid_type_name stix2/test/test_custom.py::test_parse_custom_object_type stix2/test/test_custom.py::test_parse_unregistered_custom_object_type stix2/test/test_custom.py::test_parse_unregistered_custom_object_type_w_allow_custom stix2/test/test_custom.py::test_custom_observable_object_1 stix2/test/test_custom.py::test_custom_observable_object_2 stix2/test/test_custom.py::test_custom_observable_object_3 stix2/test/test_custom.py::test_custom_observable_raises_exception stix2/test/test_custom.py::test_custom_observable_object_invalid_type_name stix2/test/test_custom.py::test_custom_observable_object_invalid_ref_property stix2/test/test_custom.py::test_custom_observable_object_invalid_refs_property stix2/test/test_custom.py::test_custom_observable_object_invalid_refs_list_property stix2/test/test_custom.py::test_custom_observable_object_invalid_valid_refs stix2/test/test_custom.py::test_custom_no_properties_raises_exception stix2/test/test_custom.py::test_custom_wrong_properties_arg_raises_exception stix2/test/test_custom.py::test_parse_unregistered_custom_observable_object stix2/test/test_custom.py::test_parse_unregistered_custom_observable_object_with_no_type stix2/test/test_custom.py::test_parse_observed_data_with_custom_observable stix2/test/test_custom.py::test_parse_invalid_custom_observable_object stix2/test/test_custom.py::test_observable_custom_property stix2/test/test_custom.py::test_observable_custom_property_invalid stix2/test/test_custom.py::test_observable_custom_property_allowed stix2/test/test_custom.py::test_custom_extension_raises_exception stix2/test/test_custom.py::test_custom_extension stix2/test/test_custom.py::test_custom_extension_wrong_observable_type stix2/test/test_custom.py::test_custom_extension_invalid_observable stix2/test/test_custom.py::test_custom_extension_invalid_type_name stix2/test/test_custom.py::test_custom_extension_no_properties stix2/test/test_custom.py::test_custom_extension_empty_properties stix2/test/test_custom.py::test_custom_extension_dict_properties stix2/test/test_custom.py::test_parse_observable_with_custom_extension stix2/test/test_custom.py::test_parse_observable_with_unregistered_custom_extension stix2/test/test_custom.py::test_register_custom_object stix2/test/test_custom.py::test_extension_property_location stix2/test/test_utils.py::test_timestamp_formatting[dttm0-2017-01-01T00:00:00Z] stix2/test/test_utils.py::test_timestamp_formatting[dttm1-2016-12-31T23:00:00Z] stix2/test/test_utils.py::test_timestamp_formatting[dttm2-2017-01-01T17:34:56Z] stix2/test/test_utils.py::test_timestamp_formatting[dttm3-2017-07-01T04:00:00Z] stix2/test/test_utils.py::test_timestamp_formatting[dttm4-2017-07-01T00:00:00Z] stix2/test/test_utils.py::test_timestamp_formatting[dttm5-2017-07-01T00:00:00.000001Z] stix2/test/test_utils.py::test_timestamp_formatting[dttm6-2017-07-01T00:00:00.000Z] stix2/test/test_utils.py::test_timestamp_formatting[dttm7-2017-07-01T00:00:00Z] stix2/test/test_utils.py::test_parse_datetime[timestamp0-dttm0] stix2/test/test_utils.py::test_parse_datetime[timestamp1-dttm1] stix2/test/test_utils.py::test_parse_datetime[2017-01-01T00:00:00Z-dttm2] stix2/test/test_utils.py::test_parse_datetime[2017-01-01T02:00:00+2:00-dttm3] stix2/test/test_utils.py::test_parse_datetime[2017-01-01T00:00:00-dttm4] stix2/test/test_utils.py::test_parse_datetime_precision[2017-01-01T01:02:03.000001-dttm0-millisecond] stix2/test/test_utils.py::test_parse_datetime_precision[2017-01-01T01:02:03.001-dttm1-millisecond] stix2/test/test_utils.py::test_parse_datetime_precision[2017-01-01T01:02:03.1-dttm2-millisecond] stix2/test/test_utils.py::test_parse_datetime_precision[2017-01-01T01:02:03.45-dttm3-millisecond] stix2/test/test_utils.py::test_parse_datetime_precision[2017-01-01T01:02:03.45-dttm4-second] stix2/test/test_utils.py::test_parse_datetime_invalid[foobar] stix2/test/test_utils.py::test_parse_datetime_invalid[1] stix2/test/test_utils.py::test_get_dict[data0] stix2/test/test_utils.py::test_get_dict[{"a": stix2/test/test_utils.py::test_get_dict[data2] stix2/test/test_utils.py::test_get_dict[data3] stix2/test/test_utils.py::test_get_dict_invalid[1] stix2/test/test_utils.py::test_get_dict_invalid[data1] stix2/test/test_utils.py::test_get_dict_invalid[data2] stix2/test/test_utils.py::test_get_dict_invalid[foobar] stix2/test/test_utils.py::test_get_type_from_id[malware--d69c8146-ab35-4d50-8382-6fc80e641d43-malware] stix2/test/test_utils.py::test_get_type_from_id[intrusion-set--899ce53f-13a0-479b-a0e4-67d46e241542-intrusion-set] stix2/test/test_utils.py::test_deduplicate stix2/test/test_utils.py::test_find_property_index[object0-tuple_to_find0-1]