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cpython/Lib/xml/etree/ElementPath.py

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#
# ElementTree
# $Id: ElementPath.py 3375 2008-02-13 08:05:08Z fredrik $
#
# limited xpath support for element trees
#
# history:
# 2003-05-23 fl created
# 2003-05-28 fl added support for // etc
# 2003-08-27 fl fixed parsing of periods in element names
# 2007-09-10 fl new selection engine
# 2007-09-12 fl fixed parent selector
# 2007-09-13 fl added iterfind; changed findall to return a list
# 2007-11-30 fl added namespaces support
# 2009-10-30 fl added child element value filter
#
# Copyright (c) 2003-2009 by Fredrik Lundh. All rights reserved.
#
# fredrik@pythonware.com
# http://www.pythonware.com
#
# --------------------------------------------------------------------
# The ElementTree toolkit is
#
# Copyright (c) 1999-2009 by Fredrik Lundh
#
# By obtaining, using, and/or copying this software and/or its
# associated documentation, you agree that you have read, understood,
# and will comply with the following terms and conditions:
#
# Permission to use, copy, modify, and distribute this software and
# its associated documentation for any purpose and without fee is
# hereby granted, provided that the above copyright notice appears in
# all copies, and that both that copyright notice and this permission
# notice appear in supporting documentation, and that the name of
# Secret Labs AB or the author not be used in advertising or publicity
# pertaining to distribution of the software without specific, written
# prior permission.
#
# SECRET LABS AB AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD
# TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANT-
# ABILITY AND FITNESS. IN NO EVENT SHALL SECRET LABS AB OR THE AUTHOR
# BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY
# DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
# WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
# ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
# OF THIS SOFTWARE.
# --------------------------------------------------------------------
# Licensed to PSF under a Contributor Agreement.
# See https://www.python.org/psf/license for licensing details.
##
# Implementation module for XPath support. There's usually no reason
# to import this module directly; the <b>ElementTree</b> does this for
# you, if needed.
##
import re
xpath_tokenizer_re = re.compile(
r"("
r"'[^']*'|\"[^\"]*\"|"
r"::|"
r"//?|"
r"\.\.|"
r"\(\)|"
r"!=|"
r"[/.*:\[\]\(\)@=])|"
r"((?:\{[^}]+\})?[^/\[\]\(\)@!=\s]+)|"
r"\s+"
)
def xpath_tokenizer(pattern, namespaces=None):
default_namespace = namespaces.get('') if namespaces else None
parsing_attribute = False
for token in xpath_tokenizer_re.findall(pattern):
ttype, tag = token
if tag and tag[0] != "{":
if ":" in tag:
prefix, uri = tag.split(":", 1)
try:
if not namespaces:
raise KeyError
yield ttype, "{%s}%s" % (namespaces[prefix], uri)
except KeyError:
raise SyntaxError("prefix %r not found in prefix map" % prefix) from None
elif default_namespace and not parsing_attribute:
yield ttype, "{%s}%s" % (default_namespace, tag)
else:
yield token
parsing_attribute = False
else:
yield token
parsing_attribute = ttype == '@'
def get_parent_map(context):
parent_map = context.parent_map
if parent_map is None:
context.parent_map = parent_map = {}
for p in context.root.iter():
for e in p:
parent_map[e] = p
return parent_map
def _is_wildcard_tag(tag):
return tag[:3] == '{*}' or tag[-2:] == '}*'
def _prepare_tag(tag):
_isinstance, _str = isinstance, str
if tag == '{*}*':
# Same as '*', but no comments or processing instructions.
# It can be a surprise that '*' includes those, but there is no
# justification for '{*}*' doing the same.
def select(context, result):
for elem in result:
if _isinstance(elem.tag, _str):
yield elem
elif tag == '{}*':
# Any tag that is not in a namespace.
def select(context, result):
for elem in result:
el_tag = elem.tag
if _isinstance(el_tag, _str) and el_tag[0] != '{':
yield elem
elif tag[:3] == '{*}':
# The tag in any (or no) namespace.
suffix = tag[2:] # '}name'
no_ns = slice(-len(suffix), None)
tag = tag[3:]
def select(context, result):
for elem in result:
el_tag = elem.tag
if el_tag == tag or _isinstance(el_tag, _str) and el_tag[no_ns] == suffix:
yield elem
elif tag[-2:] == '}*':
# Any tag in the given namespace.
ns = tag[:-1]
ns_only = slice(None, len(ns))
def select(context, result):
for elem in result:
el_tag = elem.tag
if _isinstance(el_tag, _str) and el_tag[ns_only] == ns:
yield elem
else:
raise RuntimeError(f"internal parser error, got {tag}")
return select
def prepare_child(next, token):
tag = token[1]
if _is_wildcard_tag(tag):
select_tag = _prepare_tag(tag)
def select(context, result):
def select_child(result):
for elem in result:
yield from elem
return select_tag(context, select_child(result))
else:
if tag[:2] == '{}':
tag = tag[2:] # '{}tag' == 'tag'
def select(context, result):
for elem in result:
for e in elem:
if e.tag == tag:
yield e
return select
def prepare_star(next, token):
def select(context, result):
for elem in result:
yield from elem
return select
def prepare_self(next, token):
def select(context, result):
yield from result
return select
def prepare_descendant(next, token):
try:
token = next()
except StopIteration:
return
if token[0] == "*":
tag = "*"
elif not token[0]:
tag = token[1]
else:
raise SyntaxError("invalid descendant")
if _is_wildcard_tag(tag):
select_tag = _prepare_tag(tag)
def select(context, result):
def select_child(result):
for elem in result:
for e in elem.iter():
if e is not elem:
yield e
return select_tag(context, select_child(result))
else:
if tag[:2] == '{}':
tag = tag[2:] # '{}tag' == 'tag'
def select(context, result):
for elem in result:
for e in elem.iter(tag):
if e is not elem:
yield e
return select
def prepare_parent(next, token):
def select(context, result):
# FIXME: raise error if .. is applied at toplevel?
parent_map = get_parent_map(context)
result_map = {}
for elem in result:
if elem in parent_map:
parent = parent_map[elem]
if parent not in result_map:
result_map[parent] = None
yield parent
return select
def prepare_predicate(next, token):
# FIXME: replace with real parser!!! refs:
# http://javascript.crockford.com/tdop/tdop.html
signature = []
predicate = []
while 1:
try:
token = next()
except StopIteration:
return
if token[0] == "]":
break
if token == ('', ''):
# ignore whitespace
continue
if token[0] and token[0][:1] in "'\"":
token = "'", token[0][1:-1]
signature.append(token[0] or "-")
predicate.append(token[1])
signature = "".join(signature)
# use signature to determine predicate type
if signature == "@-":
# [@attribute] predicate
key = predicate[1]
def select(context, result):
for elem in result:
if elem.get(key) is not None:
yield elem
return select
if signature == "@-='" or signature == "@-!='":
# [@attribute='value'] or [@attribute!='value']
key = predicate[1]
value = predicate[-1]
def select(context, result):
for elem in result:
if elem.get(key) == value:
yield elem
def select_negated(context, result):
for elem in result:
if (attr_value := elem.get(key)) is not None and attr_value != value:
yield elem
return select_negated if '!=' in signature else select
if signature == "-" and not re.match(r"\-?\d+$", predicate[0]):
# [tag]
tag = predicate[0]
def select(context, result):
for elem in result:
if elem.find(tag) is not None:
yield elem
return select
if signature == ".='" or signature == ".!='" or (
(signature == "-='" or signature == "-!='")
and not re.match(r"\-?\d+$", predicate[0])):
# [.='value'] or [tag='value'] or [.!='value'] or [tag!='value']
tag = predicate[0]
value = predicate[-1]
if tag:
def select(context, result):
for elem in result:
for e in elem.findall(tag):
if "".join(e.itertext()) == value:
yield elem
break
def select_negated(context, result):
for elem in result:
for e in elem.iterfind(tag):
if "".join(e.itertext()) != value:
yield elem
break
else:
def select(context, result):
for elem in result:
if "".join(elem.itertext()) == value:
yield elem
def select_negated(context, result):
for elem in result:
if "".join(elem.itertext()) != value:
yield elem
return select_negated if '!=' in signature else select
if signature == "-" or signature == "-()" or signature == "-()-":
# [index] or [last()] or [last()-index]
if signature == "-":
# [index]
index = int(predicate[0]) - 1
if index < 0:
raise SyntaxError("XPath position >= 1 expected")
else:
if predicate[0] != "last":
raise SyntaxError("unsupported function")
if signature == "-()-":
try:
index = int(predicate[2]) - 1
except ValueError:
raise SyntaxError("unsupported expression")
if index > -2:
raise SyntaxError("XPath offset from last() must be negative")
else:
index = -1
def select(context, result):
parent_map = get_parent_map(context)
for elem in result:
try:
parent = parent_map[elem]
# FIXME: what if the selector is "*" ?
elems = list(parent.findall(elem.tag))
if elems[index] is elem:
yield elem
except (IndexError, KeyError):
pass
return select
raise SyntaxError("invalid predicate")
ops = {
"": prepare_child,
"*": prepare_star,
".": prepare_self,
"..": prepare_parent,
"//": prepare_descendant,
"[": prepare_predicate,
}
_cache = {}
class _SelectorContext:
parent_map = None
def __init__(self, root):
self.root = root
# --------------------------------------------------------------------
##
# Generate all matching objects.
def iterfind(elem, path, namespaces=None):
# compile selector pattern
if path[-1:] == "/":
path = path + "*" # implicit all (FIXME: keep this?)
cache_key = (path,)
if namespaces:
cache_key += tuple(sorted(namespaces.items()))
try:
selector = _cache[cache_key]
except KeyError:
if len(_cache) > 100:
_cache.clear()
if path[:1] == "/":
raise SyntaxError("cannot use absolute path on element")
next = iter(xpath_tokenizer(path, namespaces)).__next__
try:
token = next()
except StopIteration:
return
selector = []
while 1:
try:
selector.append(ops[token[0]](next, token))
except StopIteration:
raise SyntaxError("invalid path") from None
try:
token = next()
if token[0] == "/":
token = next()
except StopIteration:
break
_cache[cache_key] = selector
# execute selector pattern
result = [elem]
context = _SelectorContext(elem)
for select in selector:
result = select(context, result)
return result
##
# Find first matching object.
def find(elem, path, namespaces=None):
return next(iterfind(elem, path, namespaces), None)
##
# Find all matching objects.
def findall(elem, path, namespaces=None):
return list(iterfind(elem, path, namespaces))
##
# Find text for first matching object.
def findtext(elem, path, default=None, namespaces=None):
try:
elem = next(iterfind(elem, path, namespaces))
return elem.text or ""
except StopIteration:
return default
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