CODEWITHSUNDEEP
pythongtkpygtk
Parin Porecha
Parin Porecha

Reputation: 563

PyGTK custom signals send a list as parameter

I'm trying to add a custom signal to a class -

class TaskBrowser(gobject.GObject):
    __list_signal__ = (gobject.SIGNAL_RUN_FIRST, gobject.TYPE_NONE, (<List datatype>,))
    __gsignals__ = {'tasks-deleted': __list_signal__}

    ...

    def on_delete_tasks(self, widget=None, tid=None):
        ...
        gobject.idle_add(self.emit, "tasks-deleted", deleted_tasks) #deleted_tasks is of type 'list'
        ...

    ...

In the __gsignals__ dict, when I state list as parameter type, I get the following error traceback -

File "/home/manhattan/GTG/Hamster_in_hands/GTG/gtk/browser/browser.py", line 61, in <module>
  class TaskBrowser(gobject.GObject):
File "/usr/lib/python2.7/site-packages/gobject/__init__.py", line 60, in __init__
  cls._type_register(cls.__dict__)
File "/usr/lib/python2.7/site-packages/gobject/__init__.py", line 115, in _type_register
  type_register(cls, namespace.get('__gtype_name__'))
TypeError: Error when calling the metaclass bases
  could not get typecode from object

I saw the list of possible parameter types, and there's no type for list

Is there a way I can pass a list as a signal parameter ?

Upvotes: 3

Views: 1106

Answers (2)

M.javid
M.javid

Reputation: 6637

In pygtk3 this error has been occured for me because import gobject directly. and fixed this error by from gi.repository import GObject. you can see details in this link.

Upvotes: 0

OdraEncoded
OdraEncoded

Reputation: 3134

The C library needs to know the C type of the parameters, for Gtk, Gdk, Gio and GLib objects the types in the wrappers will work as they mirror the C types in the Gtk and family libraries.

However, for any other type you need to pass either object or gobject.TYPE_PYOBJECT. What that means is that the on the C side a "python object" type is passed. Every object accessible from a python script is of that type, that pretty much means anything you can pass through your python script will fit an object parameter.

That also means, of course, that this feature doesn't work in python! Python relies on duck typing, that means we figure out if an object is of a type when we do stuff with it and it works. Passing the type of the parameter works for C as a way to make sure the objects passed are of the type the program needs them to be, but in python every object is of the same type in the C side so this feature becomes completely useless on the python side.

But that doesn't means it is completely useless overall. For example, in python int is an object. But not in C. If you are using property bindings, which were coded in the C side of the Gtk library, you will want to specify the appropriate type as bindings of different property types don't work.

Using C side wrapped signal handlers with object parameter types is also bound not to work, since the C side needs a specific type to function.

Upvotes: 3

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