bpo-30485: support a default prefix mapping in ElementPath by passing None as prefix (#1823)

1 files changed, 24 insertions, 9 deletions

diff --git a/Lib/xml/etree/ElementPath.py b/Lib/xml/etree/ElementPath.py
index ef32917..0e3854f 100644
--- a/Lib/xml/etree/ElementPath.py
+++ b/Lib/xml/etree/ElementPath.py
@@ -71,16 +71,22 @@ xpath_tokenizer_re = re.compile(
     )
 
 def xpath_tokenizer(pattern, namespaces=None):
+    default_namespace = namespaces.get(None) if namespaces else None
     for token in xpath_tokenizer_re.findall(pattern):
         tag = token[1]
-        if tag and tag[0] != "{" and ":" in tag:
-            try:
+        if tag and tag[0] != "{":
+            if ":" in tag:
                 prefix, uri = tag.split(":", 1)
-                if not namespaces:
-                    raise KeyError
-                yield token[0], "{%s}%s" % (namespaces[prefix], uri)
-            except KeyError:
-                raise SyntaxError("prefix %r not found in prefix map" % prefix) from None
+                try:
+                    if not namespaces:
+                        raise KeyError
+                    yield token[0], "{%s}%s" % (namespaces[prefix], uri)
+                except KeyError:
+                    raise SyntaxError("prefix %r not found in prefix map" % prefix) from None
+            elif default_namespace:
+                yield token[0], "{%s}%s" % (default_namespace, tag)
+            else:
+                yield token
         else:
             yield token
 
@@ -264,10 +270,19 @@ class _SelectorContext:
 
 def iterfind(elem, path, namespaces=None):
     # compile selector pattern
-    cache_key = (path, None if namespaces is None
-                            else tuple(sorted(namespaces.items())))
     if path[-1:] == "/":
         path = path + "*" # implicit all (FIXME: keep this?)
+
+    cache_key = (path,)
+    if namespaces:
+        if '' in namespaces:
+            raise ValueError("empty namespace prefix must be passed as None, not the empty string")
+        if None in namespaces:
+            cache_key += (namespaces[None],) + tuple(sorted(
+                item for item in namespaces.items() if item[0] is not None))
+        else:
+            cache_key += tuple(sorted(namespaces.items()))
+
     try:
         selector = _cache[cache_key]
     except KeyError: