How can I pass two arguments to Pool.starmap()?

Question

Originally, with the code I was using, Pool.map was sufficient for threading my code as there was only one argument (an, iterable) being passed in as a parameter to my function. Now, I have a requirement to pass in multiple arguments to the function and I'm having some trouble using Pool.starmap.

I attempted to use zip alongside Pool.map to no avail.

Here's my current code:

def get_links_on_page(job_title, page_num):
    page = requests.get("%s/jobs?q=%s&l=%s%%2C%s&start=%s" % (__SITE_BASE__, job_title.replace(' ', '+'), 'City', 'PROV', str(page_num*25)), verify=False)
    print(page.url)
    soup = BeautifulSoup(page.content, 'html.parser')

    return [link.a.get('href') for link in soup.find_all('div', {'class': 'title'})]


def get_all_links(job_title):
    """
    :param: job_title (string): A string representing the job's title
    """

    all_links = []
    pool = ThreadPool(processes=20)
    all_links.extend(pool.starmap(get_links_on_page, (job_title, [i for i in range(1, 5)]))) 
    pool.close()
    return all_links

This gives me an error like:

TypeError: '<=' not supported between instances of 'list' and 'int'

I also attempted to pass in the two arguments as an iterable like so:

def get_all_links(job_title):
    all_links = []
    pool = ThreadPool(processes=20)
    all_links.extend(pool.starmap(get_links_on_page, [job_title, [i for i in range(1, 5)]])) #[func(job_title, 1), func(job_title, 2), func(job_title, 3) ...]
    pool.close()
    return all_links

And that would equate to 18 arguments and thus throw an error. I'm currently reading the docs here:

https://docs.python.org/dev/library/multiprocessing.html#multiprocessing.pool.Pool.starmap

But I'm having trouble getting the syntax down..

Any help would be really appreciated!

user_9059420 · Answer

You've been on the right track with using zip(), you just need to repeat() the job_title:

list(zip(itertools.repeat("jobname"), range(1, 5)))
# [('jobname', 1), ('jobname', 2), ('jobname', 3), ('jobname', 4)]

So for your example:

from itertools import repeat

def get_all_links(job_title, n): # n would be 4 in your example
    iterable = zip(repeat(job_title), range(1, n+1))
    with ThreadPool(n) as pool:
        all_links = pool.starmap(get_links_on_page, iterable)
    return all_links

How can I pass two arguments to Pool.starmap()?

1 Answers