Showing an image when dragging any tag in HTML

Chrome and Safari support displaying a ghost image for draggable objects out of the box, Firefox does not. It's not a big deal, I'd say a matter of one event handler.

This is a sample HTML:

Drag Me!

and JavaScript code:

$(function () {
    var dragImage = document.createElement("img");
    dragImage.src = "/image/to/show/when/dragging.jpg";
    function handleDragStart(e) {
        e.dataTransfer.effectAllowed = 'move';
        e.dataTransfer.setDragImage(dragImage, e.layerX, e.layerY);
    }

    $("#draggableObject").get(0).addEventListener('dragstart', handleDragStart, false);
});

Native HTML5 Drag and Drop

MDN::dataTransfer

Line numbers in Vim

I would like to cover all aspects known for me related to the line numbers in Vim.

Command	Description
:0	move cursor to the first
:42 42gg 42G	move cursor to 42nd
:G	move cursor to the last

Show line numbers in current file

:set number

Hide line numbers in current file

:set nonumber

Computed field on TabularInline (StackedInline)

Django admin doesn't provide list_display attribute on its inline admin classes. That's right, since the only supposed view for those classes is editable form. So, to display a result of custom function's call, it needs to add the name of the function (that can be declared either on the admin or model classed) to both fields and readonly_fields.

Example:

class StatsInline(admin.TabularInline):
    model = Stats
    fields = ('clicked', 'shown', 'avg')
    readonly_fields = ('avg',)
    verbose_name = 'Stats'
    verbose_name_plural = 'Stats'
    can_delete = False

    def avg(self, obj):
        return float(obj.clicked) / obj.shown if obj.shown else 0

P.S. float conversion is needed to avoid casting result to int (e.g. 1/2=0, float(1)/2=0.5)