Raise an exception when taskwarrior has a non-zero return status.

taskw/exceptions.py

@@ -0,0 +1,8 @@
+
+
+class TaskwarriorError(Exception):
+    def __init__(self, stderr, stdout, code):
+        self.stderr = stderr.strip()
+        self.stdout = stdout.strip()
+        self.code = code
+        super(TaskwarriorError, self).__init__(self.stderr)

taskw/warrior.py

@@ -24,6 +24,7 @@
 import pprint
 
 import taskw.utils
+from taskw.exceptions import TaskwarriorError
 
 import six
 from six import with_metaclass
@@ -420,11 +421,15 @@ def _execute(self, *args):
             'rc.verbose=nothing',
             'rc.confirmation=no',
         ] + [six.text_type(arg) for arg in args]
-        return subprocess.Popen(
+        proc = subprocess.Popen(
             command,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
-        ).communicate()
+        )
+        stdout, stderr = proc.communicate()
+        if proc.returncode != 0:
+            raise TaskwarriorError(stderr, stdout, proc.returncode)
+        return stdout, stderr
 
     def _get_json(self, *args):
         encoded = self._execute(*args)[0]