valid_groups.py

import re
import typing as tp

import requests
from bs4 import BeautifulSoup

# keep groups cached since they rarely change
# groups_cache[group_id] == group_name
groups_cache: tp.Dict[int, str] = {}


def fetch_groups() -> tp.Dict[int, str]:
    global groups_cache

    if groups_cache:
        return groups_cache

    # fetch groups if they are not cached

    # regex for finding group ids in html params
    # 5 digits after 'id_group='
    group_id_re = re.compile("(?<=id_group=)\\d{5}")

    # fetch html and make soup
    html = requests.get("https://guide.herzen.spb.ru/static/schedule.php").content
    soup = BeautifulSoup(html, features="lxml")

    # get the element with the relevant information
    schedule = soup.select("td.body > div")[0]

    # get departments (institute, faculty, etc.)
    dept_names = [d.get_text() for d in schedule.select("h3 a")]
    dept_forms = schedule.find_all("div", recursive=False)

    for i in range(len(dept_names)):
        dept = dept_forms[i]

        # get forms of education (full time, part time or both)
        form_names = [d.get_text() for d in dept.find_all("h4", recursive=False)]
        form_groups = dept.find_all("ul", recursive=False)

        for j in range(len(form_names)):
            form = form_groups[j]

            # get groups
            groups = form.find_all("li", recursive=False)

            for group in groups:
                # get name and join it with dept and form names
                group_name = group.contents[0]
                group_full_name = ", ".join([dept_names[i], form_names[j], group_name])
                # find group id param in the element
                group_id = int(group_id_re.search(str(group)).group())
                # capitalize first letter and write to cache
                groups_cache[group_id] = group_full_name[0].upper() + group_full_name[1:]

    return groups_cache


# check if a group id is present among all groups
def group_id_is_valid(group_id: int) -> bool:
    # call in case groups are not fetched yet
    groups = fetch_groups()
    return group_id in groups