Description of Objects in VPython

Additional Attributes

The following attributes apply to all VPython objects:

visible If false (0), object is not displayed; e.g. ball.visible = 0
Use ball.visible = 1 to make the ball visible again.

frame Place this object into a specified frame, as in ball = sphere(frame = f1)

display When you start a VPython program, for convenience Visual creates a display window and names it scene. By default, objects you create go into that display window. You can choose to put an object in a different display like this:

scene2 = display( title = "Act IV, Scene 2" )

rod = cylinder( display = scene2 )

The function display.get_selected() returns a reference to the display in which objects are currently being created.

__class__ Name of the class of object. For example, ball.__class__ is sphere is true if ball is a sphere object. There are two underscores before and after the word class. In a list of visible objects provided by scene.objects, if obj is in this list you can determine the class of the object with obj.__class__.

__copy()__ Makes a copy of an object. There are two underscores before and after the copy(). Without any arguments, this results in creating a second object in the exact same position as the first, which is probably not what you want. The __copy__() function takes a list of keyword=value argument pairs which are applied to the new object before making it visible. For example, to clone an object from one display to another, you would execute: new_object = old_object.__copy__( display=new_display). Restriction: If the original object is within a frame, and the new object is on a different display, you must supply both a new display and a new frame for the new object (the new frame may be None). This is due to the restriction that an object may not be located within a frame that is in a separate display. The attribute __members__ used to give a list of all the object's attributes but is no longer available in VPython. Its main use was in copying objects.

Here is an example that uses the __copy()__ function. The following routine copies all of the Visual objects currently existing in one display into a previously defined second display:

def clone_universe( new_display, old_display):
        # Create a dictionary of frames in the old display
        # to the corresponding frames in the new display.
        frames = dict()
        # Initialize the lookup dictionary
        for obj in old_display.objects:
                if obj.__class__ == frame:
                        frames[obj] = obj.__copy__( frame=None, display=new_display)
        # For each old reference frame that was within another reference frame,
        # place the new reference frame within the appropriate frame in the new
        # display. Here old is an object and new is its frame in the new display.
        for old, new in frames.iteritems():
                if old.frame:
                        new.frame = frames[old.frame]
        # Copy over the universe.
        for obj in old_display.objects:
                if obj.__class__ == frame:
                        # Already taken care of above.
                        continue
                if obj.frame:
                        # Then initialize with the corresponding reference frame in the new
                        # display.
                        obj.__copy__( display=new_display, frame=frames[obj.frame])
                else:
                        # Don't need to care about the frame attribute, since it is None.
                        obj.__copy__( display=new_display)

See Controlling One or More Visual Display Windows for more information on creating and manipulating display objects.