from bs4 import BeautifulSoup

html_doc = ("<section id=\"box3\" class=\"nodisp_zero\" style=\"display: none;\">\n"
	"    <h1 id=\"box_ttl3\" style=\"display: none;\"></h1>\n"
	"    <img style=\"width: 100%; display: none;\" id=\"box_img3\" alt=\"box3\" src=\"https://s...content-available-to-author-only...s.jp/s/topics/img/dummy.png\" class=\"lazy\" data-original=\"https://s...content-available-to-author-only...s.jp/s/topics/img/201808/201808220015_box_img3_A.jpg?1533975785\">\n"
	"    <figcaption id=\"box_caption3\" style=\"display: none;\"></figcaption>\n"
	"    <div class=\"textarea clearfix\">\n"
	"        <h2 id=\"box_subttl3\" style=\"display: none;\"></h2>\n"
	"        <div class=\"fontL\" id=\"box_com3\" style=\"display: none;\"></div>\n"
	"    </div>\n"
	"</section>")
soup = BeautifulSoup(html_doc, 'html.parser')
for tag in soup.findAll(lambda tag:tag.has_attr('style')):
  tag["style"] = tag["style"].replace("display: none;", "")

print(str(soup))