Build a wallet tutorial: draft steps 1-3

1. wxPython app that shows XRPL data (once)
2. threaded app monitoring XRPL in background
3. Decode address & watch for balance

content/_code-samples/build-a-wallet/py/2_threaded.py

@@ -0,0 +1,72 @@
+# "Build a Wallet" tutorial, step 2: Watch ledger closes from a worker thread.
+
+import xrpl
+import wx
+# New dependencies
+from threading import Thread
+import wx.lib.newevent
+
+# Set up an event type to pass info from the worker thread to the main thread
+GotNewLedger, EVT_NEW_LEDGER = wx.lib.newevent.NewEvent()
+class XRPLMonitorThread(Thread):
+    """
+    A worker thread to watch for new ledger events and pass the info back to
+    the main frame to be shown in the UI. Using a thread lets us maintain the
+    responsiveness of the UI while doing work in the background.
+    """
+    def __init__(self, ws_url, notify_window):
+        Thread.__init__(self, daemon=True)
+        self.notify_window = notify_window
+        self.ws_url = ws_url
+
+    def run(self):
+        with xrpl.clients.WebsocketClient(self.ws_url) as client:
+            # Subscribe to ledger updates
+            client.send(xrpl.models.requests.Subscribe(
+                id="ledger_sub",
+                streams=[xrpl.models.requests.StreamParameter.LEDGER]
+            ))
+            # Watch for messages in the client
+            for message in client:
+                if message.get("id") == "ledger_sub":
+                    # Immediate response to our subscribe command.
+                    wx.QueueEvent(self.notify_window, GotNewLedger(data=message["result"]))
+                elif message.get("type") == "ledgerClosed":
+                    # Ongoing notifications that new ledgers have been validated.
+                    wx.QueueEvent(self.notify_window, GotNewLedger(data=message))
+                else:
+                    print("Unhandled message:", message)
+
+class TWaXLFrame(wx.Frame):
+    """
+    Tutorial Wallet for the XRP Ledger (TWaXL)
+    user interface, main frame.
+    """
+    def __init__(self, url):
+        wx.Frame.__init__(self, None, title="TWaXL", size=wx.Size(800,400))
+
+        main_panel = wx.Panel(self)
+        main_sizer = wx.BoxSizer(wx.VERTICAL)
+        main_panel.SetSizer(main_sizer)
+
+        self.st = wx.StaticText(main_panel, label="Not connected")
+        main_sizer.Add(self.st, wx.SizerFlags().Border(wx.TOP|wx.LEFT, 25))
+
+        self.Bind(EVT_NEW_LEDGER, self.update_ledger)
+        XRPLMonitorThread(url, self).start()
+
+    def update_ledger(self, event):
+        message = event.data
+        self.st.SetLabel(f"Latest validated ledger:\n"
+                         f"Ledger Index: {message['ledger_index']}\n"
+                         f"Ledger Hash: {message['ledger_hash']}")
+
+if __name__ == "__main__":
+    #JSON_RPC_URL = "https://s.altnet.rippletest.net:51234/"
+    #JSON_RPC_URL = "http://localhost:5005/"
+    WS_URL = "wss://s.altnet.rippletest.net:51233"
+
+    app = wx.App()
+    frame = TWaXLFrame(WS_URL)
+    frame.Show()
+    app.MainLoop()