markdown to html converter

import re
import mistune
from bs4 import BeautifulSoup as bs


def main():
    file = input("Name of Markdown file: ")
    while ('.md' not in file):
        print("that is not a recognized Markdown file.")
        file = input("Name of Markdown file: ")

    fileName = file.split('.')[0]
    html_doc = open(fileName+".html", 'w')

    generated_html = ("<!DOCTYPE html>" +
                      "<!--Converted via md-to-html-->" +
                      "<html><head></head><body>")

    with open(file) as f:
        content = f.readlines()
        for line in content:
            generated_html += mistune.markdown(line)

    generated_html += "</body></html>"

    # make BeautifulSoup
    soup = bs(generated_html, "html.parser")
    # prettify the html
    prettyHTML = soup.prettify()
    # write to the html doc
    html_doc.write(prettyHTML)


if __name__ == "__main__":
    main()