Change several "raise HTMLParseError" statements into assertions, as

these are really complaints about the intgrity of our own code.
HTMLParseError should be raised only for invalid input.  (Should we
turn more unrecognized constructs into exceptions, e.g. '&' not
followed by an entity or character reference?)

Also added an 'r' prefix to a regex string containing a backslash.

lib/python/TAL/HTMLParser.py

@@ -23,7 +23,7 @@ entityref = re.compile('&([a-zA-Z][-.a-zA-Z0-9]*)[^a-zA-Z0-9]')
 charref = re.compile('&#([0-9]+)[^0-9]')
 
 starttagopen = re.compile('<[a-zA-Z]')
-piopen = re.compile('<\?')
+piopen = re.compile(r'<\?')
 piclose = re.compile('>')
 endtagopen = re.compile('</[a-zA-Z]')
 special = re.compile('<![^<>]*>')
@@ -147,6 +147,7 @@ class HTMLParser:
             if i < j: self.handle_data(rawdata[i:j])
             i = self.updatepos(i, j)
             if i == n: break
+            assert rawdata[i] in "<&", "interesting.search() lied"
             if rawdata[i] == '<':
                 if starttagopen.match(rawdata, i):
                     if self.literal:
@@ -213,8 +214,6 @@ class HTMLParser:
                         k = k-1
                     i = self.updatepos(i, k)
                     continue
-            else:
-                raise HTMLParserError('neither < nor & ??', self.getpos())
             # We get here only if incomplete matches but
             # nothing else
             match = incomplete.match(rawdata, i)
@@ -237,9 +236,7 @@ class HTMLParser:
     # Internal -- parse comment, return length or -1 if not terminated
     def parse_comment(self, i):
         rawdata = self.rawdata
-        if rawdata[i:i+4] != '<!--':
-            raise HTMLParseError('unexpected call to parse_comment()',
-                                 self.getpos())
+        assert rawdata[i:i+4] == '<!--', 'unexpected call to parse_comment()'
         match = commentclose.search(rawdata, i+4)
         if not match:
             return -1
@@ -283,9 +280,7 @@ class HTMLParser:
     # Internal -- parse processing instr, return length or -1 if not terminated
     def parse_pi(self, i):
         rawdata = self.rawdata
-        if rawdata[i:i+2] != '<?':
-            raise HTMLParseError('unexpected call to parse_pi()',
-                                 self.getpos())
+        assert rawdata[i:i+2] == '<?', 'unexpected call to parse_pi()'
         match = piclose.search(rawdata, i+2)
         if not match:
             return -1
@@ -311,9 +306,7 @@ class HTMLParser:
         # Now parse the data between i+1 and j into a tag and attrs
         attrs = []
         match = tagfind.match(rawdata, i+1)
-        if not match:
-            raise HTMLParseError('unexpected call to parse_starttag()',
-                                 self.getpos())
+        assert match, 'unexpected call to parse_starttag()'
         k = match.end(0)
         self.lasttag = tag = string.lower(rawdata[i+1:k])