Is it possible to use Python to write cross-platform apps for both iOS and Android
You can try and combine brython and cordova. The Brython wiki describes how to write an Android app using Brython, which might provide the necessary information to do this also using Cordova. I haven't tested this yet, but it sounds promising. You should however be aware that due to its nature, Brython cannot support x86-compiled packages such as OpenCV (see e.g. here). On the other hand, if you know a bit about JavaScript / HTML5, you can use the WebView native functions, e.g. http://www.brython.info/gallery/three.html.