Issue reported by user when using gtk2.py example. Even though window is realized and get_window_handle() returns a valid handle, the browser creation fails due to some race condition in GTK/X11. Showing window before browser is embedded resolves the problem.

In the wxpython.py example it is required on Linux to show window before embedding, but in this case it is mandatory because window handle returned is 0. In the gtk2.py example window handle is valid, but the X11 window seems not to be yet ready for CEF browser to be embedded in it.

Issue in details reported on the Forum:
https://groups.google.com/d/topic/cefpython/IKfi_yrIOmY/discussion