Beginner Python OOP web scraper
Use list comprehensions instead of creating empty array and appending to it in a for loop. It's both faster and more readable.

@staticmethod
def get_comments(soup):
    return [
        Comment(*DatabazeKnih.parse_comment(comment)
        for comment in soup.find_all('div', {'class': 'komholdu'})
    ]


But If would argue that you don't need classes here at all.

from bs4 import BeautifulSoup
from collections import namedtuple
import requests as r


Book = namedtuple('Book', 'title rating text authors year comments')
Comment = namedtuple('Comment', 'user text date')
PAGE_URL = 'http://www.databazeknih.cz/'


def search(name):
    page = r.get(PAGE_URL + 'search', params=dict(q=name, stranka='search')).text
    link = BeautifulSoup(page, 'html.parser').find(type='book').attrs['href']
    book_page = r.get(PAGE_URL + link, params=dict(show='alldesc')).text
    return book_info(book_page)


def book_info(book_page):
    soup = BeautifulSoup(book_page, 'html.parser')
    title = soup.find(itemprop='name').string
    rating = soup.findAll('a', {'class': 'bpoints'})[0].string
    text = soup.find(itemprop='description').string
    authors = [elem.string for elem in soup.find(itemprop='author').find_all('a')]
    year = soup.find(itemprop='datePublished').string
    comments = [
        Comment(*parse_comment(elem))
        for elem in soup.find_all('div', {'class': 'komholdu'})
    ]
    return Book(title, rating, text, authors, year, comments)


def parse_comment(comment):
    user = comment.find('a').string
    text = comment.find('p', {'class': 'odtopm new2 justify'}).text
    date = comment.find('span', {'class': 'pozn_lightest odleft_pet'}).string
    return user, text, date


My suggestions are.

Use requests library, It's more pythonic than urllib.

Use namedtuples instead of classes where possible. Easier to read and to write. If you need to add functionality you can inherit from namedtuple.

Don't write one liner get_this get_that functions. It's useful when you're hiding some implementation, but hiding one or two lines - it's useless and it's even a bit less readable (when you would need this implementation).

What you're doing with function name get_authors you can do just as easy with giving a variable self-explanatory name like authors = .... Everybody would understand that next one or two lines (if it's a comprehension) is getting authors in some way and they can read this lines if they want details.

Also get_book_info means suggesting it's loading or getting something from somewhere. In java it just means that this is some property, but in python we have @property decorator and don't need getters and setters so get is used when you're loading something. Instead it's more accurate to think of it as pure function that takes html and outputs Book. You can call it make_book_info, def book_info_from(html): or just book_info.