Add onbeforeclose.py snippet

examples/snippets/onbeforeclose.py

@@ -0,0 +1,24 @@
+# Implement LifespanHandler.OnBeforeClose to execute custom
+# code before browser window closes.
+
+from cefpython3 import cefpython as cef
+
+
+def main():
+    cef.Initialize()
+    browser = cef.CreateBrowserSync(url="https://www.google.com/",
+                                    window_title="OnBeforeClose")
+    browser.SetClientHandler(LifespanHandler())
+    cef.MessageLoop()
+    del browser
+    cef.Shutdown()
+
+
+class LifespanHandler(object):
+    def OnBeforeClose(self, browser):
+        print("Browser ID: {}".format(browser.GetIdentifier()))
+        print("Browser will close and app will exit")
+
+
+if __name__ == '__main__':
+    main()