Convert numpy types to their native python types

I don't know exactly why but for some reason the json encoder in python3 can't encode some of the numpy datetypes. Now I simply converted the numpy data types (http://docs.scipy.org/doc/numpy/user/basics.types.html) to the respective python types.

airflow/utils.py

@@ -2,7 +2,7 @@
 from builtins import str, input, object
 from past.builtins import basestring
 from copy import copy
-from datetime import datetime, timedelta
+from datetime import datetime, date, timedelta
 from dateutil.relativedelta import relativedelta  # for doctest
 from email.mime.text import MIMEText
 from email.mime.multipart import MIMEMultipart
@@ -29,6 +29,8 @@
 from sqlalchemy import event, exc
 from sqlalchemy.pool import Pool
 
+import numpy
+
 from airflow import settings
 from airflow.configuration import conf
 
@@ -619,9 +621,19 @@ def chain(*tasks):
 
 class AirflowJsonEncoder(json.JSONEncoder):
     def default(self, obj):
+        # convert dates and numpy objects in a json serializable format
         if isinstance(obj, datetime):
             return obj.strftime('%Y-%m-%dT%H:%M:%SZ')
         elif isinstance(obj, date):
             return obj.strftime('%Y-%m-%d')
+        elif type(obj) in [numpy.int_, numpy.intc, numpy.intp, numpy.int8,
+         numpy.int16, numpy.int32, numpy.int64, numpy.uint8, numpy.uint16, numpy.uint32, numpy.uint64]:
+            return int(obj)
+        elif type(obj) in [numpy.bool_]:
+            return bool(obj)
+        elif type(obj) in [numpy.float_, numpy.float16, numpy.float32, numpy.float64,
+         numpy.complex_, numpy.complex64, numpy.complex128,:
+            return float(obj)
+
         # Let the base class default method raise the TypeError
         return json.JSONEncoder.default(self, obj)