Q:

Using gpointer with Python and GObject introspection

I am learning about Python and Gtk 3, using GObject introspection.  I have done some samples, and I am begining to understant how it works.  But there is one thing I can't understand, How can I pass a gpointer param? 
I trying to use a function who receive a buffer (with gpointer), and I always end with this message:
could not convert value for property `pixels' from LP_c_ubyte to gpointer
(LP_c_ubyte was my last try, but I have prove a lot of types)

A:

You can't pass a pointer in GObject introspection.  If the introspected function is one you wrote yourself, then you should annotate your parameter documentation with, for example, (array length=buflen), where buflen is the name for the parameter that gives the length of the buffer.  See the linked page for more information. 
If the function is in a library that you didn't write yourself, either look around in the API for a more introspection-friendly function, or file a bug with the library.  APIs using bare gpointers shouldn't even be exposed to Python.