bootstrap-pull-by-size.scss

$directions: right, left;
$sizes: xs, sm, md, lg;
@each $direction in $directions {

  @each $size in $sizes {

    .pull-#{$direction}-#{$size}{

      @if($size == xs){
        @media (min-width: $screen-xs-min) {
          float:#{$direction};
        }
      }
      @else if($size == sm){
        @media (min-width: $screen-sm-min) {
          float:#{$direction};
        }
      }
      @else if($size == md){
        @media (min-width: $screen-md-min) {
          float:#{$direction};
        }
      }
      @else if($size == lg){
        @media (min-width: $screen-lg-min) {
          float:#{$direction};
        }
      }
    }
  }
}