columnizer.py

from collections import namedtuple
from itertools import islice

LineProperties = namedtuple('LineProperties', 'column_widths, spacing')

def get_line_properties(items, spacing=2, max_line_width=80):
    item_widths = [len(item) for item in items]
    num_items = len(item_widths)
    column_widths = []
    line_width = 0
    column_size = 1
    start_index, stop_index = 0, column_size
    while start_index < num_items:
        # This loop repeatedly adds a new column (or more specifically: a new
        # column size) to an "imaginary" line. It starts with a column size
        # (i.e. the number of items per column) of 1. 

        # Every time when max_line_width is exceeded the loop will increase the
        # the column size, reset its computed values and start again with the
        # first item. This is done until all items have been passed. The loop
        # should then have found a sufficient configuration of column widths to
        # use for LineProperties and terminates.
        column_width = max(islice(item_widths, start_index, stop_index))
        line_width += column_width
        if line_width > max_line_width:
            if not column_widths:
                # Special case: first column includes an item > max_line_width
                # => do not fail but just use the width limit as the result.
                column_widths = [max_line_width]
                break
            column_widths = []
            line_width = 0
            column_size += 1
            start_index, stop_index = 0, column_size
        else:
            column_widths.append(column_width)
            line_width += spacing
            start_index, stop_index = stop_index, stop_index + column_size
    return LineProperties(column_widths, spacing)