bootstrap v4 print columns (based on bootstrap v4's _grid-framework) (https://github.com/twbs/bootstrap/issues/16800#issuecomment-172406940)

_print-grid-framwork.scss

// Framework print grid generation (for v4.0.0-beta.2)
//
// Used only to generate the correct number of grid classes given
// any value of `$grid-columns`.
// import bootstrap prior to this mixin to set the various variables and mixins needed/used.

@mixin make-print-grid-columns($columns: $grid-columns, $gutter: $grid-gutter-width, $name: "pr") {
  @media print {
    // Common properties
    %grid-column-print {
      position: relative;
      width: 100%;
      min-height: 1px; // Prevent columns from collapsing when empty
      padding-right: ($gutter / 2);
      padding-left: ($gutter / 2);
    }

    // Allow columns to stretch full width below their breakpoints
    @for $i from 1 through $columns {
      .col-#{$name}-#{$i} {
        @extend %grid-column-print;
      }
    }
    .col-#{$name} {
      @extend %grid-column-print;
    }

    // Provide basic `.col-{bp}` classes for equal-width flexbox columns
    .col-#{$name} {
      flex-basis: 0;
      flex-grow: 1;
      max-width: 100%;
    }
    .col-#{$name}-auto {
      flex: 0 0 auto;
      width: auto;
    }

    @for $i from 1 through $columns {
      .col-#{$name}-#{$i} {
        @include make-col($i, $columns);
      }
    }

    .order-#{$name}-first {
      order: -1;
    }

    @for $i from 1 through $columns {
      .order-#{$name}-#{$i} {
        order: $i;
      }
    }

    // `$columns - 1` because offsetting by the width of an entire row isn't possible
    @for $i from 0 through ($columns - 1) {
      .offset-#{$name}-#{$i} {
        @include make-col-offset($i, $columns)
      }
    }
  }
}