Hammer the official UK chart from a known starting point and write out a CSV of title, artist and highest position achieved

chart.py

import csv
from lxml.html import parse

inf = float('inf')
base_uri = 'http://www.officialcharts.com'
start_page = '/charts/singles-chart/20150828/7501/'
positions = {}

def parse_page(page):
    tree = parse(base_uri + page)
    for row in tree.xpath('//table[@class="chart-positions"]/tr'):
        track = row.xpath('./td/div[@class="track"]')

        if track == []: continue

        position = int(row.xpath('./td[4]/text()')[0])
        title = row.xpath('./td[3]/div/div[2]/div[1]/a/text()')[0]
        artist = row.xpath('./td[3]/div/div[2]/div[2]/a/text()')[0]

        track = (title, artist)

        last_known_position = positions.get(track, inf)

        if position < last_known_position:
            positions[track] = position


    next_links = tree.xpath('//a[@class="next chart-date-directions"]/@href')

    if len(next_links) > 0:
        return next_links[0]

page = start_page
count = 0

while page:
    page = parse_page(page)
    count += 1

with open('/tmp/chart.csv', 'wb') as csvfile:
    w = csv.writer(csvfile, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)

    for track, position in positions.items():
        w.writerow([track[1], track[0], position])