Allow widget value to be accessed as an attribute

See feature request #116. This is a bit kludgy, and is read-only so far,
but it seems to work and should be faster than calling
gp_widget_get_value or CameraWidget.get_value

setup.py

@@ -1,6 +1,6 @@
 # python-gphoto2 - Python interface to libgphoto2
 # http://github.com/jim-easterbrook/python-gphoto2
-# Copyright (C) 2014-20  Jim Easterbrook  jim@jim-easterbrook.me.uk
+# Copyright (C) 2014-21  Jim Easterbrook  jim@jim-easterbrook.me.uk
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -26,7 +26,7 @@
 import sys
 
 # python-gphoto2 version
-version = '2.2.5'
+version = '2.3.0'
 
 # get gphoto2 library config
 cmd = ['pkg-config', '--modversion', 'libgphoto2']

src/gphoto2/widget.i

@@ -1,6 +1,6 @@
 // python-gphoto2 - Python interface to libgphoto2
 // http://github.com/jim-easterbrook/python-gphoto2
-// Copyright (C) 2014-20  Jim Easterbrook  jim@jim-easterbrook.me.uk
+// Copyright (C) 2014-21  Jim Easterbrook  jim@jim-easterbrook.me.uk
 //
 // This program is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
@@ -18,6 +18,7 @@
 %module(package="gphoto2") widget
 
 %include "common/preamble.i"
+%include <attribute.i>
 
 %rename(CameraWidget) _CameraWidget;
 
@@ -199,6 +200,45 @@ int gp_widget_get_value(CameraWidget *widget, int *value);
 // Ignore original void* version
 %ignore gp_widget_get_value(CameraWidget *widget, void *value);
 
+// Add a 'value' attribute to CameraWidget
+%attribute(_CameraWidget, PyObject*, value, value_get);
+%ignore _CameraWidget_value_get;
+
+%{
+// Undefine %attribute macro's version of _CameraWidget_value_get
+#undef _CameraWidget_value_get
+
+// Define our own _CameraWidget_value_get function
+static PyObject* _CameraWidget_value_get(CameraWidget *widget) {
+  int error;
+  CameraWidgetType type;
+  union {
+    int int_val;
+    float flt_val;
+    char* str_val;
+  } value;
+  value.str_val = NULL;
+  error = gp_widget_get_value(widget, &value);
+  if (error < GP_OK) goto fail;
+  error = gp_widget_get_type(widget, &type);
+  if (error < GP_OK) goto fail;
+  switch (type) {
+    case GP_WIDGET_DATE:
+    case GP_WIDGET_TOGGLE:
+      return SWIG_From_int(value.int_val);
+    case GP_WIDGET_RANGE:
+      return SWIG_From_float(value.flt_val);
+    default:
+      if (value.str_val) return PyString_FromString(value.str_val);
+      Py_INCREF(Py_None);
+      return Py_None;
+  }
+fail:
+  PyErr_SetObject(PyExc_GPhoto2Error, PyInt_FromLong(error));
+  return NULL;
+}
+%}
+
 // function to allow python iter() to be called with python object
 #if defined(SWIGPYTHON_BUILTIN)
 %ignore make_iterator;