Python exceptions can now be handled via QML

callCoro/callBackendCoro can now take onSuccess(result) and
onError(type, args, errorObject) callbacks.

src/qml/Python.qml

@@ -14,18 +14,20 @@ Python {
         return call_sync("APP.backend." + name, args)
     }
 
-    function callCoro(name, args=[], callback=null) {
+    function callCoro(name, args=[], onSuccess=null, onError=null) {
         let uuid = Math.random() + "." + name
 
-        pendingCoroutines[uuid] = callback || function() {}
+        pendingCoroutines[uuid] = {onSuccess, onError}
         call("APP.call_backend_coro", [name, uuid, args])
     }
 
-    function callClientCoro(accountId, name, args=[], callback=null) {
+    function callClientCoro(
+        accountId, name, args=[], onSuccess=null, onError=null
+    ) {
         callCoro("wait_until_client_exists", [accountId], () => {
             let uuid = Math.random() + "." + name
 
-            pendingCoroutines[uuid] = callback || function() {}
+            pendingCoroutines[uuid] = {onSuccess, onError}
             call("APP.call_client_coro", [accountId, name, uuid, args])
         })
     }

src/qml/event_handlers.js

@@ -13,8 +13,20 @@ function onAlertRequested() {
 }
 
 
-function onCoroutineDone(uuid, result) {
-    py.pendingCoroutines[uuid](result)
+function onCoroutineDone(uuid, result, error) {
+    let onSuccess = py.pendingCoroutines[uuid].onSuccess
+    let onError   = py.pendingCoroutines[uuid].onError
+
+    if (error) {
+        let type = py.getattr(py.getattr(error, "__class__"), "__name__")
+        let args = py.getattr(error, "args")
+
+        onError ?
+        onError(type, args, error) :
+        console.error(uuid + ": " + type + ": " + args)
+
+    } else if (onSuccess) { onSuccess(result) }
+
     delete pendingCoroutines[uuid]
 }