Clarify that the Headers class is a Sequence

This is both in the docs (via the changelog) and by inheriting from
the Sequence ABC. As the Sequence ABC has a __iter__ method another is
not required.

h11/_headers.py

@@ -1,4 +1,5 @@
 import re
+from collections.abc import Sequence
 
 from ._abnf import field_name, field_value
 from ._util import bytesify, LocalProtocolError, validate
@@ -62,7 +63,7 @@
 _field_value_re = re.compile(field_value.encode("ascii"))
 
 
-class Headers:
+class Headers(Sequence):
     """
     A list-like interface that allows iterating over headers as byte-pairs
     of (lowercased-name, value).
@@ -92,10 +93,6 @@ class Headers:
     def __init__(self, full_items):
         self._full_items = full_items
 
-    def __iter__(self):
-        for _, name, value in self._full_items:
-            yield name, value
-
     def __bool__(self):
         return bool(self._full_items)
 

newsfragments/112.feature.rst

@@ -0,0 +1,3 @@
+Clarify that the Headers class is a Sequence and inherit from the
+collections Sequence abstract base class to also indicate this (and
+gain the mixin methods). See also #104.