Script to generate CSS rules for columns of a grid system.

grid-generator.py

#!/usr/bin/env python2.7
# -*- coding: utf-8 -*-

# Number of digits after the dot to be output in the CSS rule.
PRECISION = 8

def generate_grid(columns, className, collapseThreshold=1):
    """
    Generates CSS code for a grid system.
    columns           - The number of columns the grid consists of.
    className         - The name of each column rule. The name will be
                        suffix with a dash and the column number.
    collapseThreshold - The number of columns sharing a width value.
    """
    if collapseThreshold > columns or columns % collapseThreshold != 0:
        exit(1)

    # Preprocessing to get the formatting right.

    # The percentage values for each column as strings aligned by the dot.
    widths = []
    # The most digits after the dot of a width value.
    maxPrecision = 0
    for i in range(1, columns + 1):
        if i % collapseThreshold == 0:
            precision = PRECISION
            width = ''.join(('{:>', str(precision + 4), '.', str(precision), 'f}')).format(100.0 / columns * i)
            for j in range(len(width) - 1, 3, -1):
                if width[j] != '0':
                    break
                precision -= 1

            if precision > maxPrecision:
                maxPrecision = precision

            widths.append(width[:3 + precision + (0 if precision == 0 else 1)])

    stylesheet = []
    for i in range(columns):
        stylesheet.append(className if className[0] == '.' else '.{}'.format(className))
        stylesheet.append('-')
        stylesheet.append(str(i + 1))
        if (i + 1) % collapseThreshold == 0:
            stylesheet.append(' ' * (2 if columns > 9 and i < 9 else 1))
            if collapseThreshold > 1:
                stylesheet.append(' ')
            stylesheet.append('{ width: ')
            widthLength = len(widths[i / collapseThreshold])
            if maxPrecision > 0:
                if widthLength == 3:
                    widthLength += maxPrecision + 1
                else:
                    widthLength += (maxPrecision - (widthLength - 4))
            widthLength += 2 # for '%;'

            stylesheet.append(''.join(('{:<', str(widthLength), '}')).format('{}%;'.format(widths[i / collapseThreshold])))
            stylesheet.append(' }')
        else:
            stylesheet.append(',')
        stylesheet.append('\n')

    return ''.join(stylesheet)


if __name__ == "__main__":
    print generate_grid(16, 'column')