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# -*- coding: utf-8 -*-
"""
cssselect.xpath
===============
Translation of parsed CSS selectors to XPath expressions.
:copyright: (c) 2007-2012 Ian Bicking and contributors.
See AUTHORS for more details.
:license: BSD, see LICENSE for more details.
"""
import sys
import re
from cssselect.parser import parse, parse_series, SelectorError
if sys.version_info[0] < 3:
_basestring = basestring
_unicode = unicode
else:
_basestring = str
_unicode = str
def _unicode_safe_getattr(obj, name, default=None):
# getattr() with a non-ASCII name fails on Python 2.x
name = name.encode('ascii', 'replace').decode('ascii')
return getattr(obj, name, default)
class ExpressionError(SelectorError, RuntimeError):
"""Unknown or unsupported selector (eg. pseudo-class)."""
#### XPath Helpers
class XPathExpr(object):
def __init__(self, path='', element='*', condition='', star_prefix=False):
self.path = path
self.element = element
self.condition = condition
def __str__(self):
path = _unicode(self.path) + _unicode(self.element)
if self.condition:
path += '[%s]' % self.condition
return path
def __repr__(self):
return '%s[%s]' % (self.__class__.__name__, self)
def add_condition(self, condition):
if self.condition:
self.condition = '%s and (%s)' % (self.condition, condition)
else:
self.condition = condition
return self
def add_name_test(self):
if self.element == '*':
# We weren't doing a test anyway
return
self.add_condition(
"name() = %s" % GenericTranslator.xpath_literal(self.element))
self.element = '*'
def add_star_prefix(self):
"""
Append '*/' to the path to keep the context constrained
to a single parent.
"""
self.path += '*/'
def join(self, combiner, other):
path = _unicode(self) + combiner
# Any "star prefix" is redundant when joining.
if other.path != '*/':
path += other.path
self.path = path
self.element = other.element
self.condition = other.condition
return self
split_at_single_quotes = re.compile("('+)").split
# The spec is actually more permissive than that, but don’t bother.
# This is just for the fast path.
# http://www.w3.org/TR/REC-xml/#NT-NameStartChar
is_safe_name = re.compile('^[a-zA-Z_][a-zA-Z0-9_.-]*$').match
# Test that the string is not empty and does not contain whitespace
is_non_whitespace = re.compile(r'^[^ \t\r\n\f]+$').match
#### Translation
class GenericTranslator(object):
"""
Translator for "generic" XML documents.
Everything is case-sensitive, no assumption is made on the meaning
of element names and attribute names.
"""
####
#### HERE BE DRAGONS
####
#### You are welcome to hook into this to change some behavior,
#### but do so at your own risks.
#### Until it has received a lot more work and review,
#### I reserve the right to change this API in backward-incompatible ways
#### with any minor version of cssselect.
#### See https://github.com/scrapy/cssselect/pull/22
#### -- Simon Sapin.
####
combinator_mapping = {
' ': 'descendant',
'>': 'child',
'+': 'direct_adjacent',
'~': 'indirect_adjacent',
}
attribute_operator_mapping = {
'exists': 'exists',
'=': 'equals',
'~=': 'includes',
'|=': 'dashmatch',
'^=': 'prefixmatch',
'$=': 'suffixmatch',
'*=': 'substringmatch',
'!=': 'different', # XXX Not in Level 3 but meh
}
#: The attribute used for ID selectors depends on the document language:
#: http://www.w3.org/TR/selectors/#id-selectors
id_attribute = 'id'
#: The attribute used for ``:lang()`` depends on the document language:
#: http://www.w3.org/TR/selectors/#lang-pseudo
lang_attribute = 'xml:lang'
#: The case sensitivity of document language element names,
#: attribute names, and attribute values in selectors depends
#: on the document language.
#: http://www.w3.org/TR/selectors/#casesens
#:
#: When a document language defines one of these as case-insensitive,
#: cssselect assumes that the document parser makes the parsed values
#: lower-case. Making the selector lower-case too makes the comparaison
#: case-insensitive.
#:
#: In HTML, element names and attributes names (but not attribute values)
#: are case-insensitive. All of lxml.html, html5lib, BeautifulSoup4
#: and HTMLParser make them lower-case in their parse result, so
#: the assumption holds.
lower_case_element_names = False
lower_case_attribute_names = False
lower_case_attribute_values = False
# class used to represent and xpath expression
xpathexpr_cls = XPathExpr
def css_to_xpath(self, css, prefix='descendant-or-self::'):
"""Translate a *group of selectors* to XPath.
Pseudo-elements are not supported here since XPath only knows
about "real" elements.
:param css:
A *group of selectors* as an Unicode string.
:param prefix:
This string is prepended to the XPath expression for each selector.
The default makes selectors scoped to the context node’s subtree.
:raises:
:class:`SelectorSyntaxError` on invalid selectors,
:class:`ExpressionError` on unknown/unsupported selectors,
including pseudo-elements.
:returns:
The equivalent XPath 1.0 expression as an Unicode string.
"""
return ' | '.join(self.selector_to_xpath(selector, prefix,
translate_pseudo_elements=True)
for selector in parse(css))
def selector_to_xpath(self, selector, prefix='descendant-or-self::',
translate_pseudo_elements=False):
"""Translate a parsed selector to XPath.
:param selector:
A parsed :class:`Selector` object.
:param prefix:
This string is prepended to the resulting XPath expression.
The default makes selectors scoped to the context node’s subtree.
:param translate_pseudo_elements:
Unless this is set to ``True`` (as :meth:`css_to_xpath` does),
the :attr:`~Selector.pseudo_element` attribute of the selector
is ignored.
It is the caller's responsibility to reject selectors
with pseudo-elements, or to account for them somehow.
:raises:
:class:`ExpressionError` on unknown/unsupported selectors.
:returns:
The equivalent XPath 1.0 expression as an Unicode string.
"""
tree = getattr(selector, 'parsed_tree', None)
if not tree:
raise TypeError('Expected a parsed selector, got %r' % (selector,))
xpath = self.xpath(tree)
assert isinstance(xpath, self.xpathexpr_cls) # help debug a missing 'return'
if translate_pseudo_elements and selector.pseudo_element:
xpath = self.xpath_pseudo_element(xpath, selector.pseudo_element)
return (prefix or '') + _unicode(xpath)
def xpath_pseudo_element(self, xpath, pseudo_element):
"""Translate a pseudo-element.
Defaults to not supporting pseudo-elements at all,
but can be overridden by sub-classes.
"""
raise ExpressionError('Pseudo-elements are not supported.')
@staticmethod
def xpath_literal(s):
s = _unicode(s)
if "'" not in s:
s = "'%s'" % s
elif '"' not in s:
s = '"%s"' % s
else:
s = "concat(%s)" % ','.join([
(("'" in part) and '"%s"' or "'%s'") % part
for part in split_at_single_quotes(s) if part
])
return s
def xpath(self, parsed_selector):
"""Translate any parsed selector object."""
type_name = type(parsed_selector).__name__
method = getattr(self, 'xpath_%s' % type_name.lower(), None)
if method is None:
raise ExpressionError('%s is not supported.' % type_name)
return method(parsed_selector)
# Dispatched by parsed object type
def xpath_combinedselector(self, combined):
"""Translate a combined selector."""
combinator = self.combinator_mapping[combined.combinator]
method = getattr(self, 'xpath_%s_combinator' % combinator)
return method(self.xpath(combined.selector),
self.xpath(combined.subselector))
def xpath_negation(self, negation):
xpath = self.xpath(negation.selector)
sub_xpath = self.xpath(negation.subselector)
sub_xpath.add_name_test()
if sub_xpath.condition:
return xpath.add_condition('not(%s)' % sub_xpath.condition)
else:
return xpath.add_condition('0')
def xpath_function(self, function):
"""Translate a functional pseudo-class."""
method = 'xpath_%s_function' % function.name.replace('-', '_')
method = _unicode_safe_getattr(self, method, None)
if not method:
raise ExpressionError(
"The pseudo-class :%s() is unknown" % function.name)
return method(self.xpath(function.selector), function)
def xpath_pseudo(self, pseudo):
"""Translate a pseudo-class."""
method = 'xpath_%s_pseudo' % pseudo.ident.replace('-', '_')
method = _unicode_safe_getattr(self, method, None)
if not method:
# TODO: better error message for pseudo-elements?
raise ExpressionError(
"The pseudo-class :%s is unknown" % pseudo.ident)
return method(self.xpath(pseudo.selector))
def xpath_attrib(self, selector):
"""Translate an attribute selector."""
operator = self.attribute_operator_mapping[selector.operator]
method = getattr(self, 'xpath_attrib_%s' % operator)
if self.lower_case_attribute_names:
name = selector.attrib.lower()
else:
name = selector.attrib
safe = is_safe_name(name)
if selector.namespace:
name = '%s:%s' % (selector.namespace, name)
safe = safe and is_safe_name(selector.namespace)
if safe:
attrib = '@' + name
else:
attrib = 'attribute::*[name() = %s]' % self.xpath_literal(name)
if selector.value is None:
value = None
elif self.lower_case_attribute_values:
value = selector.value.value.lower()
else:
value = selector.value.value
return method(self.xpath(selector.selector), attrib, value)
def xpath_class(self, class_selector):
"""Translate a class selector."""
# .foo is defined as [class~=foo] in the spec.
xpath = self.xpath(class_selector.selector)
return self.xpath_attrib_includes(
xpath, '@class', class_selector.class_name)
def xpath_hash(self, id_selector):
"""Translate an ID selector."""
xpath = self.xpath(id_selector.selector)
return self.xpath_attrib_equals(xpath, '@id', id_selector.id)
def xpath_element(self, selector):
"""Translate a type or universal selector."""
element = selector.element
if not element:
element = '*'
safe = True
else:
safe = is_safe_name(element)
if self.lower_case_element_names:
element = element.lower()
if selector.namespace:
# Namespace prefixes are case-sensitive.
# http://www.w3.org/TR/css3-namespace/#prefixes
element = '%s:%s' % (selector.namespace, element)
safe = safe and is_safe_name(selector.namespace)
xpath = self.xpathexpr_cls(element=element)
if not safe:
xpath.add_name_test()
return xpath
# CombinedSelector: dispatch by combinator
def xpath_descendant_combinator(self, left, right):
"""right is a child, grand-child or further descendant of left"""
return left.join('/descendant-or-self::*/', right)
def xpath_child_combinator(self, left, right):
"""right is an immediate child of left"""
return left.join('/', right)
def xpath_direct_adjacent_combinator(self, left, right):
"""right is a sibling immediately after left"""
xpath = left.join('/following-sibling::', right)
xpath.add_name_test()
return xpath.add_condition('position() = 1')
def xpath_indirect_adjacent_combinator(self, left, right):
"""right is a sibling after left, immediately or not"""
return left.join('/following-sibling::', right)
# Function: dispatch by function/pseudo-class name
def xpath_nth_child_function(self, xpath, function, last=False,
add_name_test=True):
try:
a, b = parse_series(function.arguments)
except ValueError:
raise ExpressionError("Invalid series: '%r'" % function.arguments)
# From https://www.w3.org/TR/css3-selectors/#structural-pseudos:
#
# :nth-child(an+b)
# an+b-1 siblings before
#
# :nth-last-child(an+b)
# an+b-1 siblings after
#
# :nth-of-type(an+b)
# an+b-1 siblings with the same expanded element name before
#
# :nth-last-of-type(an+b)
# an+b-1 siblings with the same expanded element name after
#
# So,
# for :nth-child and :nth-of-type
#
# count(preceding-sibling::<nodetest>) = an+b-1
#
# for :nth-last-child and :nth-last-of-type
#
# count(following-sibling::<nodetest>) = an+b-1
#
# therefore,
# count(...) - (b-1) ≡ 0 (mod a)
#
# if a == 0:
# ~~~~~~~~~~
# count(...) = b-1
#
# if a < 0:
# ~~~~~~~~~
# count(...) - b +1 <= 0
# -> count(...) <= b-1
#
# if a > 0:
# ~~~~~~~~~
# count(...) - b +1 >= 0
# -> count(...) >= b-1
# work with b-1 instead
b_min_1 = b - 1
# early-exit condition 1:
# ~~~~~~~~~~~~~~~~~~~~~~~
# for a == 1, nth-*(an+b) means n+b-1 siblings before/after,
# and since n ∈ {0, 1, 2, ...}, if b-1<=0,
# there is always an "n" matching any number of siblings (maybe none)
if a == 1 and b_min_1 <=0:
return xpath
# early-exit condition 2:
# ~~~~~~~~~~~~~~~~~~~~~~~
# an+b-1 siblings with a<0 and (b-1)<0 is not possible
if a < 0 and b_min_1 < 0:
return xpath.add_condition('0')
# `add_name_test` boolean is inverted and somewhat counter-intuitive:
#
# nth_of_type() calls nth_child(add_name_test=False)
if add_name_test:
nodetest = '*'
else:
nodetest = '%s' % xpath.element
# count siblings before or after the element
if not last:
siblings_count = 'count(preceding-sibling::%s)' % nodetest
else:
siblings_count = 'count(following-sibling::%s)' % nodetest
# special case of fixed position: nth-*(0n+b)
# if a == 0:
# ~~~~~~~~~~
# count(***-sibling::***) = b-1
if a == 0:
return xpath.add_condition('%s = %s' % (siblings_count, b_min_1))
expr = []
if a > 0:
# siblings count, an+b-1, is always >= 0,
# so if a>0, and (b-1)<=0, an "n" exists to satisfy this,
# therefore, the predicate is only interesting if (b-1)>0
if b_min_1 > 0:
expr.append('%s >= %s' % (siblings_count, b_min_1))
else:
# if a<0, and (b-1)<0, no "n" satisfies this,
# this is tested above as an early exist condition
# otherwise,
expr.append('%s <= %s' % (siblings_count, b_min_1))
# operations modulo 1 or -1 are simpler, one only needs to verify:
#
# - either:
# count(***-sibling::***) - (b-1) = n = 0, 1, 2, 3, etc.,
# i.e. count(***-sibling::***) >= (b-1)
#
# - or:
# count(***-sibling::***) - (b-1) = -n = 0, -1, -2, -3, etc.,
# i.e. count(***-sibling::***) <= (b-1)
# we we just did above.
#
if abs(a) != 1:
# count(***-sibling::***) - (b-1) ≡ 0 (mod a)
left = siblings_count
# apply "modulo a" on 2nd term, -(b-1),
# to simplify things like "(... +6) % -3",
# and also make it positive with |a|
b_neg = (-b_min_1) % abs(a)
if b_neg != 0:
b_neg = '+%s' % b_neg
left = '(%s %s)' % (left, b_neg)
expr.append('%s mod %s = 0' % (left, a))
xpath.add_condition(' and '.join(expr))
return xpath
def xpath_nth_last_child_function(self, xpath, function):
return self.xpath_nth_child_function(xpath, function, last=True)
def xpath_nth_of_type_function(self, xpath, function):
if xpath.element == '*':
raise ExpressionError(
"*:nth-of-type() is not implemented")
return self.xpath_nth_child_function(xpath, function,
add_name_test=False)
def xpath_nth_last_of_type_function(self, xpath, function):
if xpath.element == '*':
raise ExpressionError(
"*:nth-of-type() is not implemented")
return self.xpath_nth_child_function(xpath, function, last=True,
add_name_test=False)
def xpath_contains_function(self, xpath, function):
# Defined there, removed in later drafts:
# http://www.w3.org/TR/2001/CR-css3-selectors-20011113/#content-selectors
if function.argument_types() not in (['STRING'], ['IDENT']):
raise ExpressionError(
"Expected a single string or ident for :contains(), got %r"
% function.arguments)
value = function.arguments[0].value
return xpath.add_condition(
'contains(., %s)' % self.xpath_literal(value))
def xpath_lang_function(self, xpath, function):
if function.argument_types() not in (['STRING'], ['IDENT']):
raise ExpressionError(
"Expected a single string or ident for :lang(), got %r"
% function.arguments)
value = function.arguments[0].value
return xpath.add_condition(
"lang(%s)" % (self.xpath_literal(value)))
# Pseudo: dispatch by pseudo-class name
def xpath_root_pseudo(self, xpath):
return xpath.add_condition("not(parent::*)")
# CSS immediate children (CSS ":scope > div" to XPath "child::div" or "./div")
# Works only at the start of a selector
# Needed to get immediate children of a processed selector in Scrapy
# for product in response.css('.product'):
# description = product.css(':scope > div::text').get()
def xpath_scope_pseudo(self, xpath):
return xpath.add_condition("1")
def xpath_first_child_pseudo(self, xpath):
return xpath.add_condition('count(preceding-sibling::*) = 0')
def xpath_last_child_pseudo(self, xpath):
return xpath.add_condition('count(following-sibling::*) = 0')
def xpath_first_of_type_pseudo(self, xpath):
if xpath.element == '*':
raise ExpressionError(
"*:first-of-type is not implemented")
return xpath.add_condition('count(preceding-sibling::%s) = 0' % xpath.element)
def xpath_last_of_type_pseudo(self, xpath):
if xpath.element == '*':
raise ExpressionError(
"*:last-of-type is not implemented")
return xpath.add_condition('count(following-sibling::%s) = 0' % xpath.element)
def xpath_only_child_pseudo(self, xpath):
return xpath.add_condition('count(parent::*/child::*) = 1')
def xpath_only_of_type_pseudo(self, xpath):
if xpath.element == '*':
raise ExpressionError(
"*:only-of-type is not implemented")
return xpath.add_condition('count(parent::*/child::%s) = 1' % xpath.element)
def xpath_empty_pseudo(self, xpath):
return xpath.add_condition("not(*) and not(string-length())")
def pseudo_never_matches(self, xpath):
"""Common implementation for pseudo-classes that never match."""
return xpath.add_condition("0")
xpath_link_pseudo = pseudo_never_matches
xpath_visited_pseudo = pseudo_never_matches
xpath_hover_pseudo = pseudo_never_matches
xpath_active_pseudo = pseudo_never_matches
xpath_focus_pseudo = pseudo_never_matches
xpath_target_pseudo = pseudo_never_matches
xpath_enabled_pseudo = pseudo_never_matches
xpath_disabled_pseudo = pseudo_never_matches
xpath_checked_pseudo = pseudo_never_matches
# Attrib: dispatch by attribute operator
def xpath_attrib_exists(self, xpath, name, value):
assert not value
xpath.add_condition(name)
return xpath
def xpath_attrib_equals(self, xpath, name, value):
xpath.add_condition('%s = %s' % (name, self.xpath_literal(value)))
return xpath
def xpath_attrib_different(self, xpath, name, value):
# FIXME: this seems like a weird hack...
if value:
xpath.add_condition('not(%s) or %s != %s'
% (name, name, self.xpath_literal(value)))
else:
xpath.add_condition('%s != %s'
% (name, self.xpath_literal(value)))
return xpath
def xpath_attrib_includes(self, xpath, name, value):
if is_non_whitespace(value):
xpath.add_condition(
"%s and contains(concat(' ', normalize-space(%s), ' '), %s)"
% (name, name, self.xpath_literal(' '+value+' ')))
else:
xpath.add_condition('0')
return xpath
def xpath_attrib_dashmatch(self, xpath, name, value):
# Weird, but true...
xpath.add_condition('%s and (%s = %s or starts-with(%s, %s))' % (
name,
name, self.xpath_literal(value),
name, self.xpath_literal(value + '-')))
return xpath
def xpath_attrib_prefixmatch(self, xpath, name, value):
if value:
xpath.add_condition('%s and starts-with(%s, %s)' % (
name, name, self.xpath_literal(value)))
else:
xpath.add_condition('0')
return xpath
def xpath_attrib_suffixmatch(self, xpath, name, value):
if value:
# Oddly there is a starts-with in XPath 1.0, but not ends-with
xpath.add_condition(
'%s and substring(%s, string-length(%s)-%s) = %s'
% (name, name, name, len(value)-1, self.xpath_literal(value)))
else:
xpath.add_condition('0')
return xpath
def xpath_attrib_substringmatch(self, xpath, name, value):
if value:
# Attribute selectors are case sensitive
xpath.add_condition('%s and contains(%s, %s)' % (
name, name, self.xpath_literal(value)))
else:
xpath.add_condition('0')
return xpath
class HTMLTranslator(GenericTranslator):
"""
Translator for (X)HTML documents.
Has a more useful implementation of some pseudo-classes based on
HTML-specific element names and attribute names, as described in
the `HTML5 specification`_. It assumes no-quirks mode.
The API is the same as :class:`GenericTranslator`.
.. _HTML5 specification: http://www.w3.org/TR/html5/links.html#selectors
:param xhtml:
If false (the default), element names and attribute names
are case-insensitive.
"""
lang_attribute = 'lang'
def __init__(self, xhtml=False):
self.xhtml = xhtml # Might be useful for sub-classes?
if not xhtml:
# See their definition in GenericTranslator.
self.lower_case_element_names = True
self.lower_case_attribute_names = True
def xpath_checked_pseudo(self, xpath):
# FIXME: is this really all the elements?
return xpath.add_condition(
"(@selected and name(.) = 'option') or "
"(@checked "
"and (name(.) = 'input' or name(.) = 'command')"
"and (@type = 'checkbox' or @type = 'radio'))")
def xpath_lang_function(self, xpath, function):
if function.argument_types() not in (['STRING'], ['IDENT']):
raise ExpressionError(
"Expected a single string or ident for :lang(), got %r"
% function.arguments)
value = function.arguments[0].value
return xpath.add_condition(
"ancestor-or-self::*[@lang][1][starts-with(concat("
# XPath 1.0 has no lower-case function...
"translate(@%s, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', "
"'abcdefghijklmnopqrstuvwxyz'), "
"'-'), %s)]"
% (self.lang_attribute, self.xpath_literal(value.lower() + '-')))
def xpath_link_pseudo(self, xpath):
return xpath.add_condition("@href and "
"(name(.) = 'a' or name(.) = 'link' or name(.) = 'area')")
# Links are never visited, the implementation for :visited is the same
# as in GenericTranslator
def xpath_disabled_pseudo(self, xpath):
# http://www.w3.org/TR/html5/section-index.html#attributes-1
return xpath.add_condition('''
(
@disabled and
(
(name(.) = 'input' and @type != 'hidden') or
name(.) = 'button' or
name(.) = 'select' or
name(.) = 'textarea' or
name(.) = 'command' or
name(.) = 'fieldset' or
name(.) = 'optgroup' or
name(.) = 'option'
)
) or (
(
(name(.) = 'input' and @type != 'hidden') or
name(.) = 'button' or
name(.) = 'select' or
name(.) = 'textarea'
)
and ancestor::fieldset[@disabled]
)
''')
# FIXME: in the second half, add "and is not a descendant of that
# fieldset element's first legend element child, if any."
def xpath_enabled_pseudo(self, xpath):
# http://www.w3.org/TR/html5/section-index.html#attributes-1
return xpath.add_condition('''
(
@href and (
name(.) = 'a' or
name(.) = 'link' or
name(.) = 'area'
)
) or (
(
name(.) = 'command' or
name(.) = 'fieldset' or
name(.) = 'optgroup'
)
and not(@disabled)
) or (
(
(name(.) = 'input' and @type != 'hidden') or
name(.) = 'button' or
name(.) = 'select' or
name(.) = 'textarea' or
name(.) = 'keygen'
)
and not (@disabled or ancestor::fieldset[@disabled])
) or (
name(.) = 'option' and not(
@disabled or ancestor::optgroup[@disabled]
)
)
''')
# FIXME: ... or "li elements that are children of menu elements,
# and that have a child element that defines a command, if the first
# such element's Disabled State facet is false (not disabled)".
# FIXME: after ancestor::fieldset[@disabled], add "and is not a
# descendant of that fieldset element's first legend element child,
# if any."