Add support for serializing decimals

Lambda supports serializing decimals to json,
so we need to support that as well in chalice local.

chalice/local.py

@@ -4,6 +4,7 @@
 
 """
 import json
+import decimal
 import functools
 from collections import namedtuple
 from BaseHTTPServer import HTTPServer
@@ -22,6 +23,14 @@
 ServerCls = Callable[..., 'HTTPServer']
 
 
+def handle_decimals(obj):
+    # Lambda will automatically serialize decimals so we need
+    # to support that as well.
+    if isinstance(obj, decimal.Decimal):
+        return float(obj)
+    return obj
+
+
 class RouteMatcher(object):
     def __init__(self, route_urls):
         # type: (List[str]) -> None
@@ -134,7 +143,7 @@ def _do_invoke_view_function(self, lambda_event):
 
     def _send_http_response(self, lambda_event, response, status_code=200):
         # type: (EventType, Any, int) -> None
-        json_response = json.dumps(response)
+        json_response = json.dumps(response, default=handle_decimals)
         self.send_response(status_code)
         self.send_header('Content-Length', str(len(json_response)))
         self.send_header('Content-Type', 'application/json')

tests/unit/test_local.py

@@ -1,5 +1,6 @@
 from chalice import local, BadRequestError
 import json
+import decimal
 import pytest
 from pytest import fixture
 from StringIO import StringIO
@@ -56,6 +57,10 @@ def patch():
     def badrequest():
         raise BadRequestError('bad-request')
 
+    @demo.route('/decimals')
+    def decimals():
+        return decimal.Decimal('100')
+
     return demo
 
 
@@ -156,6 +161,11 @@ def test_can_support_patch_method(handler):
     handler.do_PATCH()
     assert _get_body_from_response_stream(handler) == {'patch': True}
 
+def test_can_support_decimals(handler):
+    set_current_request(handler, method='GET', path='/decimals')
+    handler.do_PATCH()
+    assert _get_body_from_response_stream(handler) == 100
+
 
 def test_unsupported_methods_raise_error(handler):
     set_current_request(handler, method='POST', path='/index')