fetch_remote_oeis_entry.py

import urllib.request
import time
import logging

logger = logging.getLogger(__name__)

class BadOeisResponse(Exception):
    def __init__(self, message):
        self.message = message
    def __str__(self):
        return self.message

class FetchResult:
    def __init__(self, oeis_id, timestamp, main_content, bfile_content):
        self.oeis_id       = oeis_id
        self.timestamp     = timestamp
        self.main_content  = main_content
        self.bfile_content = bfile_content

def fetch_url(url):
    with urllib.request.urlopen(url) as response:
        return response.read().decode(response.headers.get_content_charset())

def main_content_ok(content):

    # A proper response has 5 header lines, content, and 2 footer lines:
    #
    # lines[0]     # Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/
    # lines[1]     (empty line)
    # lines[2]     Search: id:aXXXXXX
    # lines[3]     Showing 1-1 of 1
    # lines[4]     (empty line)
    # lines[5:-2]  --- actual content directives are here ---
    # lines[-2]    (empty line)
    # lines[-1]    # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE
    #
    # We simply check the fourth line to assess the correctness of the response.

    lines = content.split("\n")
    content_ok = lines[3].strip() == "Showing 1-1 of 1"

    return content_ok

def fetch_remote_oeis_entry(oeis_id, fetch_bfile_flag):

    # We fetch a raw version of the OEIS entry, which is easy to parse.

    main_url  = "http://oeis.org/search?q=id:A{oeis_id:06d}&fmt=text".format(oeis_id = oeis_id)
    bfile_url = "http://oeis.org/A{oeis_id:06d}/b{oeis_id:06d}.txt".format(oeis_id = oeis_id)

    timestamp = time.time()

    main_content = fetch_url(main_url)

    if not main_content_ok(main_content):
        raise BadOeisResponse("OEIS server response indicates failure (url: )".format(main_url))

    bfile_content = fetch_url(bfile_url) if fetch_bfile_flag else None

    return FetchResult(oeis_id, timestamp, main_content, bfile_content)