columnizer.py

from __future__ import division

from collections import namedtuple
from itertools import count
from math import ceil

try:
    range = xrange
except NameError:
    pass

def columnize(items, spacing=2, max_line_width=80):
    line_properties = get_line_properties(items, spacing, max_line_width)
    formatter = Formatter(line_properties, items)
    return '\n'.join(formatter.line_strings)

def get_line_properties(items, spacing, max_line_width):
    for value in (spacing, max_line_width):
        if not isinstance(value, int) or value < 0:
            msg = 'spacing and max_line_width must be non-negative integers'
            raise ValueError(msg)
    item_widths = [len(item) for item in items]
    if max(item_widths) >= max_line_width:
        return LineProperties([max_line_width], spacing)
    num_items = len(item_widths)
    for chunk_size in count(1):
        column_widths = [max(item_widths[i : i + chunk_size])
                         for i in range(0, num_items, chunk_size)]
        line_width = sum(column_widths) + (len(column_widths) - 1) * spacing
        if line_width <= max_line_width:
            break
    return LineProperties(column_widths, spacing)

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

class Formatter(object):
    def __init__(self, line_properties, items=[]):
        self.line_properties = line_properties
        self.items = items

    @property
    def line_strings(self):
        num_lines = int(ceil(len(self.items) / self.num_columns))
        template = self.get_line_template()
        for i in range(num_lines):
            line_items = self.items[i::num_lines]
            try:
                yield template % tuple(line_items)
            except TypeError:
                # raised if last line contains too few items for line template
                # -> re-generate template for real number of items
                template = self.get_line_template(len(line_items))
                yield template % tuple(line_items)

    @property
    def num_columns(self):
        return len(self.line_properties.column_widths)

    def get_line_template(self, max_items=-1):
        if max_items < 0 or max_items > self.num_columns:
            max_items = self.num_columns
        specs = ('%%-%ds' % width
                 for width in self.line_properties.column_widths[:max_items])
        return (self.line_properties.spacing * ' ').join(specs)