How to make python webcrawler infinite and record link once

With the help of thenewboston I was able to create a nice little web crawler in python. After watching his videos I played around with it and added a couple of things to it. I've tried to make it infinite as in it will get every link on every link every recorded, but I have failed in doing so. I also have a problem of recording the same link more than once? How would I go about fixing this problem?

Thank you in advance, this is my code.

import requests
from bs4 import BeautifulSoup

def spider(max_pages):
    page = 1
    while page <= max_pages:
        url = ''
        source_code = requests.get(url)
        plain_text = source_code.text
        soup = BeautifulSoup(plain_text, "html.parser")
        for link in soup.findAll("a"):
            href = link.get("href")
            title = link.get("title")
            links = []
            #print(href)
            #print(title)
            try:
                get_single_user_data(href)
            except:
                pass
        page += 1

def get_single_user_data(user_url):
    source_code = requests.get(user_url)
    plain_text = source_code.text
    soup = BeautifulSoup(plain_text, "html.parser")
    #for item_name in soup.findAll('span', {'id':'mm-saleDscPrc'}):
    #   print(item_name.string)
    for link in soup.findAll("a"):
        href = link.get("href")
        print(href)


spider(1)