cmark

 # -*- coding: utf-8 -*-
 from html.parser import HTMLParser
 import urllib
 
 try:
     from html.parser import HTMLParseError
 except ImportError:
     # HTMLParseError was removed in Python 3.5. It could never be
     # thrown, so we define a placeholder instead.
     class HTMLParseError(Exception):
         pass
 
 from html.entities import name2codepoint
 import sys
 import re
 import html
 
 # Normalization code, adapted from
 # https://github.com/karlcow/markdown-testsuite/
 significant_attrs = ["alt", "href", "src", "title"]
 whitespace_re = re.compile('\s+')
 class MyHTMLParser(HTMLParser):
     def __init__(self):
         HTMLParser.__init__(self)
         self.convert_charrefs = False
         self.last = "starttag"
         self.in_pre = False
         self.output = ""
         self.last_tag = ""
     def handle_data(self, data):
         after_tag = self.last == "endtag" or self.last == "starttag"
         after_block_tag = after_tag and self.is_block_tag(self.last_tag)
         if after_tag and self.last_tag == "br":
             data = data.lstrip('\n')
         if not self.in_pre:
             data = whitespace_re.sub(' ', data)
         if after_block_tag and not self.in_pre:
             if self.last == "starttag":
                 data = data.lstrip()
             elif self.last == "endtag":
                 data = data.strip()
         self.output += data
         self.last = "data"
     def handle_endtag(self, tag):
         if tag == "pre":
             self.in_pre = False
         elif self.is_block_tag(tag):
             self.output = self.output.rstrip()
         self.output += "</" + tag + ">"
         self.last_tag = tag
         self.last = "endtag"
     def handle_starttag(self, tag, attrs):
         if tag == "pre":
             self.in_pre = True
         if self.is_block_tag(tag):
             self.output = self.output.rstrip()
         self.output += "<" + tag
         # For now we don't strip out 'extra' attributes, because of
         # raw HTML test cases.
         # attrs = filter(lambda attr: attr[0] in significant_attrs, attrs)
         if attrs:
             attrs.sort()
             for (k,v) in attrs:
                 self.output += " " + k
                 if v in ['href','src']:
                     self.output += ("=" + '"' +
                             urllib.quote(urllib.unquote(v), safe='/') + '"')
                 elif v != None:
                     self.output += ("=" + '"' + html.escape(v,quote=True) + '"')
         self.output += ">"
         self.last_tag = tag
         self.last = "starttag"
     def handle_startendtag(self, tag, attrs):
         """Ignore closing tag for self-closing """
         self.handle_starttag(tag, attrs)
         self.last_tag = tag
         self.last = "endtag"
     def handle_comment(self, data):
         self.output += '<!--' + data + '-->'
         self.last = "comment"
     def handle_decl(self, data):
         self.output += '<!' + data + '>'
         self.last = "decl"
     def unknown_decl(self, data):
         self.output += '<!' + data + '>'
         self.last = "decl"
     def handle_pi(self,data):
         self.output += '<?' + data + '>'
         self.last = "pi"
     def handle_entityref(self, name):
         try:
             c = chr(name2codepoint[name])
         except KeyError:
             c = None
         self.output_char(c, '&' + name + ';')
         self.last = "ref"
     def handle_charref(self, name):
         try:
             if name.startswith("x"):
                 c = chr(int(name[1:], 16))
             else:
                 c = chr(int(name))
         except ValueError:
                 c = None
         self.output_char(c, '&' + name + ';')
         self.last = "ref"
     # Helpers.
     def output_char(self, c, fallback):
         if c == '<':
             self.output += "&lt;"
         elif c == '>':
             self.output += "&gt;"
         elif c == '&':
             self.output += "&amp;"
         elif c == '"':
             self.output += "&quot;"
         elif c == None:
             self.output += fallback
         else:
             self.output += c
 
     def is_block_tag(self,tag):
         return (tag in ['article', 'header', 'aside', 'hgroup', 'blockquote',
             'hr', 'iframe', 'body', 'li', 'map', 'button', 'object', 'canvas',
             'ol', 'caption', 'output', 'col', 'p', 'colgroup', 'pre', 'dd',
             'progress', 'div', 'section', 'dl', 'table', 'td', 'dt',
             'tbody', 'embed', 'textarea', 'fieldset', 'tfoot', 'figcaption',
             'th', 'figure', 'thead', 'footer', 'tr', 'form', 'ul',
             'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'video', 'script', 'style'])
 
 def normalize_html(html):
     r"""
     Return normalized form of HTML which ignores insignificant output
     differences:
 
     Multiple inner whitespaces are collapsed to a single space (except
     in pre tags):
 
         >>> normalize_html("<p>a  \t b</p>")
         '<p>a b</p>'
 
         >>> normalize_html("<p>a  \t\nb</p>")
         '<p>a b</p>'
 
     * Whitespace surrounding block-level tags is removed.
 
         >>> normalize_html("<p>a  b</p>")
         '<p>a b</p>'
 
         >>> normalize_html(" <p>a  b</p>")
         '<p>a b</p>'
 
         >>> normalize_html("<p>a  b</p> ")
         '<p>a b</p>'
 
         >>> normalize_html("\n\t<p>\n\t\ta  b\t\t</p>\n\t")
         '<p>a b</p>'
 
         >>> normalize_html("<i>a  b</i> ")
         '<i>a b</i> '
 
     * Self-closing tags are converted to open tags.
 
         >>> normalize_html("<br />")
         '<br>'
 
     * Attributes are sorted and lowercased.
 
         >>> normalize_html('<a title="bar" HREF="foo">x</a>')
         '<a href="foo" title="bar">x</a>'
 
     * References are converted to unicode, except that '<', '>', '&', and
       '"' are rendered using entities.
 
         >>> normalize_html("&forall;&amp;&gt;&lt;&quot;")
         '\u2200&amp;&gt;&lt;&quot;'
 
     """
     html_chunk_re = re.compile("(\<!\[CDATA\[.*?\]\]\>|\<[^>]*\>|[^<]+)")
     try:
         parser = MyHTMLParser()
         # We work around HTMLParser's limitations parsing CDATA
         # by breaking the input into chunks and passing CDATA chunks
         # through verbatim.
         for chunk in re.finditer(html_chunk_re, html):
             if chunk.group(0)[:8] == "<![CDATA":
                 parser.output += chunk.group(0)
             else:
                 parser.feed(chunk.group(0))
         parser.close()
         return parser.output
     except HTMLParseError as e:
         sys.stderr.write("Normalization error: " + e.msg + "\n")
         return html  # on error, return unnormalized HTML