PyGTK, like other toolkits, gives you ways of invoking widgets, such as the DIALOG_MODAL flag passed to dialogs, that require a response from the user before the rest of the application can continue. In Python, as in other languages, it is good style to use modal interface elements as little as possible.

Every modal interaction is a place where your application is forcing a particular workflow on the user. While this is sometime unavoidable, as a general rule it is backwards; the application should be adapting itself to the user's preferred workflow instead.

A particularly common case of this, which ought to be much less so is confirmation prompts. Every confirmation prompt is a place where you should support an undo operation instead; the GIMP, the application GTK was originally built for, avoids many operations that would otherwise requite a stop-and-check with the user by having an undo command that can unwind any operation it does.