Apply suggestions from code review

Co-authored-by: Bénédikt Tran <[email protected]>

Author: lyc8503

Doc/library/http.server.rst

@@ -213,14 +213,17 @@ provides three different variants:
       readable description of the error.  The *explain* argument can be used to
       provide more detailed information about the error; it will be formatted
       using the :attr:`error_message_format` attribute and emitted, after
-      a complete set of headers, as the response body.  The *extra_headers*
-      argument can be a key-value tuple list which specifies extra headers to
-      be sent in the response.  The :attr:`responses` attribute holds the
-      default values for *message* and *explain* that will be used if no value
-      is provided; for unknown codes the default value for both is the string
-      ``???``. The body will be empty if the method is HEAD or the response
-      code is one of the following: :samp:`1{xx}`, ``204 No Content``,
-      ``205 Reset Content``, ``304 Not Modified``.
+      a complete set of headers, as the response body.
+
+      The *extra_headers* argument can be a key-value tuple list which
+      specifies additional headers to be sent in the response (for
+      instance, ``[("Content-Range", "bytes 3-14/42")]``).
+
+      The :attr:`responses` attribute holds the default values for *message*
+      and *explain* that will be used if no value is provided; for unknown codes
+      the default value for both is the string ``???``. The body will be empty if
+      the method is HEAD or the response code is one of the following: :samp:`1{xx}`,
+      ``204 No Content``, ``205 Reset Content``, or ``304 Not Modified``.
 
       .. versionchanged:: 3.4
          The error response includes a Content-Length header.

Lib/http/server.py

@@ -132,7 +132,7 @@
 """
 
 DEFAULT_ERROR_CONTENT_TYPE = "text/html;charset=utf-8"
-RANGE_REGEX_PATTERN = re.compile(r'bytes=(\d*)-(\d*)$', re.IGNORECASE | re.ASCII)
+RANGE_REGEX_PATTERN = re.compile(r'bytes=(\d*)-(\d*)$', re.ASCII | re.IGNORECASE)
 
 class HTTPServer(socketserver.TCPServer):
 
@@ -495,8 +495,8 @@ def send_error(self, code, message=None, explain=None, extra_headers=None):
             self.send_header("Content-Type", self.error_content_type)
             self.send_header('Content-Length', str(len(body)))
         if extra_headers is not None:
-            for (keyword, value) in extra_headers:
-                self.send_header(keyword, value)
+            for name, value in extra_headers:
+                self.send_header(name, value)
         self.end_headers()
 
         if self.command != 'HEAD' and body:
@@ -779,9 +779,9 @@ def send_head(self):
             if self._range:
                 start, end = self._range
                 if start is None:
-                    # `end` here means suffix length
                     # parse_range() collapses (None, None) to None
-                    # and thus `end` can not be None here
+                    assert end is not None
+                    # `end` here means suffix length
                     start = max(0, fs.st_size - end)
                     end = fs.st_size - 1
                 if start >= fs.st_size:
@@ -958,8 +958,10 @@ def guess_type(self, path):
 
     def parse_range(self):
         """Return a tuple of (start, end) representing the range header in
-        the HTTP request. If the range header is missing or not resolvable,
-        None is returned. This only supports single part ranges.
+        the HTTP request. If the range header is missing, not resolvable,
+        or trivial (namely "byte=-"), this returns None.
+
+        This currently only supports single part ranges.
 
         """
         range_header = self.headers.get('range')