Add support for JSON string configuration casting (#43)

* Add new JSON config casting
* Preparing a minor release with JSON cast support
* Remove pypy3 support because it is breaking at Travis

CHANGES.txt

@@ -1,3 +1,8 @@
+2.2.0
+=====
+
+  - Add new cast `config.json` for JSON configurations
+
 2.1.0
 =====
 

docs/source/casts.rst

@@ -10,6 +10,7 @@ Buitin Casts
    objects (alias to Python's ``ast.literal_eval``).
 #. ``config.list`` - converts comma separated strings into lists.
 #. ``config.tuple`` - converts comma separated strings into tuples.
+#. ``config.json`` - unserialize a string with JSON object into Python.
 #. ``config.option`` - get a return value based on specific options:
 
 .. code-block:: python

prettyconf/casts.py

@@ -1,3 +1,5 @@
+import json
+
 from .exceptions import InvalidConfiguration
 
 
@@ -93,3 +95,11 @@ def __call__(self, value):
             return self.options[value]
         except KeyError:
             raise InvalidConfiguration("Invalid option {!r}".format(value))
+
+
+class JSON(AbstractCast):
+    def __call__(self, value):
+        try:
+            return json.loads(value)
+        except json.JSONDecodeError as ex:
+            raise InvalidConfiguration('Invalid option {!r}'.format(value)) from ex

prettyconf/configuration.py

@@ -2,7 +2,7 @@
 import os
 import sys
 
-from .casts import Boolean, List, Option, Tuple
+from .casts import Boolean, JSON, List, Option, Tuple
 from .exceptions import UnknownConfiguration
 from .loaders import Environment, RecursiveSearch
 
@@ -24,6 +24,7 @@ class Configuration(object):
     tuple = Tuple()
     option = Option
     eval = staticmethod(ast.literal_eval)
+    json = JSON()
 
     def __init__(self, loaders=None):
         self._recursive_search = None

tests/test_casts.py

@@ -1,7 +1,7 @@
 import pytest
 
 from prettyconf import config
-from prettyconf.casts import Boolean, List, Option, Tuple
+from prettyconf.casts import Boolean, JSON, List, Option, Tuple
 from prettyconf.exceptions import InvalidConfiguration
 
 
@@ -104,3 +104,20 @@ def test_fail_invalid_option_config():
 
 def test_if_cast_is_unbounded():
     assert config.eval("None") is None
+
+
+@pytest.mark.parametrize('value,result', [
+    ('"string"', 'string'),
+    ('["obj1", "obj2"]', ['obj1', 'obj2']),
+    ('{"key": "value"}', {'key': 'value'}),
+    ('null', None),
+])
+def test_basic_json_cast_values(value, result):
+    json = JSON()
+    assert json(value) == result
+
+
+def test_fail_invalid_json_config():
+    json = JSON()
+    with pytest.raises(InvalidConfiguration):
+        json('invalid')