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Fix :nth-*(an+b) pseudo-classes selectors for negative a's #42

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Fix :nth-*(an+b) pseudo-classes selectors for negative a's #42

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7c7d1a6
Fix :nth-*(an+b) pseudo-classes selectors for negative a's
redapple Jul 23, 2014
fa02721
Add more tests for *-last-*(an+1)
redapple Jul 7, 2016
cca9529
Remove FIXME comment
redapple Jul 7, 2016
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82 changes: 63 additions & 19 deletions cssselect/xpath.py
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Original file line number Diff line number Diff line change
Expand Up @@ -379,37 +379,81 @@ def xpath_nth_child_function(self, xpath, function, last=False,
if add_name_test:
xpath.add_name_test()
xpath.add_star_prefix()
if a == 0:
if last:
b = 'last() - %s' % b
return xpath.add_condition('position() = %s' % b)
# non-last
# --------
# position() = an+b
# -> position() - b = an
#
# if a < 0:
# position() - b <= 0
# -> position() <= b
#
# last
# ----
# last() - position() = an+b -1
# -> last() - position() - b +1 = an
#
# if a < 0:
# last() - position() - b +1 <= 0
# -> position() >= last() - b +1
#
# -b +1 = -(b-1)
if last:
# FIXME: I'm not sure if this is right
a = -a
b = -b
b = b - 1
if b > 0:
b_neg = str(-b)
else:
b_neg = '+%s' % (-b)
if a == 0:
if last:
# http://www.w3.org/TR/selectors/#nth-last-child-pseudo
# The :nth-last-child(an+b) pseudo-class notation represents
# an element that has an+b-1 siblings after it in the document tree
#
# last() - position() = an+b-1
# -> position() = last() -b +1 (for a==0)
#
if b == 0:
b = 'last()'
else:
b = 'last() %s' % b_neg
return xpath.add_condition('position() = %s' % b)
if a != 1:
expr = ['(position() %s) mod %s = 0' % (b_neg, a)]
# last() - position() - b +1 = an
if last:
left = 'last() - position()'
# position() - b = an
else:
left = 'position()'
if b != 0:
left = '%s %s' % (left, b_neg)
if last or b != 0:
left = '(%s)' % left
expr = ['%s mod %s = 0' % (left, a)]
else:
expr = []
if b >= 0:
expr.append('position() >= %s' % b)
elif b < 0 and last:
expr.append('position() < (last() %s)' % b)
if last:
if b == 0:
right = 'last()'
else:
right = 'last() %s' % b_neg
if a > 0:
expr.append('(position() <= %s)' % right)
else:
expr.append('(position() >= %s)' % right)
else:
# position() > 0 so if b < 0, then position() > b
# also, position() >= 1 always
if b > 1:
if a > 0:
expr.append('position() >= %s' % b)
else:
expr.append('position() <= %s' % b)

expr = ' and '.join(expr)
if expr:
xpath.add_condition(expr)
return xpath
# FIXME: handle an+b, odd, even
# an+b means every-a, plus b, e.g., 2n+1 means odd
# 0n+b means b
# n+0 means a=1, i.e., all elements
# an means every a elements, i.e., 2n means even
# -n means -1n
# -1n+6 means elements 6 and previous

def xpath_nth_last_child_function(self, xpath, function):
return self.xpath_nth_child_function(xpath, function, last=True)
Expand Down
49 changes: 36 additions & 13 deletions tests/test_cssselect.py
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Original file line number Diff line number Diff line change
Expand Up @@ -336,19 +336,36 @@ def xpath(css):
"@hreflang = 'en' or starts-with(@hreflang, 'en-'))]")
assert xpath('e:nth-child(1)') == (
"*/*[name() = 'e' and (position() = 1)]")
assert xpath('e:nth-child(3n+2)') == (
"*/*[name() = 'e' and ((position() -2) mod 3 = 0 and position() >= 2)]")
assert xpath('e:nth-child(3n-2)') == (
"*/*[name() = 'e' and ((position() +2) mod 3 = 0)]")
assert xpath('e:nth-child(-n+6)') == (
"*/*[name() = 'e' and ((position() -6) mod -1 = 0 and position() <= 6)]")
assert xpath('e:nth-last-child(1)') == (
"*/*[name() = 'e' and (position() = last() - 1)]")
"*/*[name() = 'e' and (position() = last())]")
assert xpath('e:nth-last-child(2n)') == (
"*/*[name() = 'e' and ("
"(last() - position() +1) mod 2 = 0 and (position() <= last() +1))]")
assert xpath('e:nth-last-child(2n+1)') == (
"*/*[name() = 'e' and ("
"(last() - position()) mod 2 = 0 and (position() <= last()))]")
assert xpath('e:nth-last-child(2n+2)') == (
"*/*[name() = 'e' and ("
"(position() +2) mod -2 = 0 and position() < (last() -2))]")
"(last() - position() -1) mod 2 = 0 and (position() <= last() -1))]")
assert xpath('e:nth-last-child(3n+1)') == (
"*/*[name() = 'e' and ("
"(last() - position()) mod 3 = 0 and (position() <= last()))]")
# represents the two last e elements
assert xpath('e:nth-last-child(-n+2)') == (
"*/*[name() = 'e' and ("
"(last() - position() -1) mod -1 = 0 and (position() >= last() -1))]")
assert xpath('e:nth-of-type(1)') == (
"*/e[position() = 1]")
assert xpath('e:nth-last-of-type(1)') == (
"*/e[position() = last() - 1]")
assert xpath('e:nth-last-of-type(1)') == (
"*/e[position() = last() - 1]")
"*/e[position() = last()]")
assert xpath('div e:nth-last-of-type(1) .aclass') == (
"div/descendant-or-self::*/e[position() = last() - 1]"
"div/descendant-or-self::*/e[position() = last()]"
"/descendant-or-self::*/*[@class and contains("
"concat(' ', normalize-space(@class), ' '), ' aclass ')]")
assert xpath('e:first-child') == (
Expand Down Expand Up @@ -381,7 +398,7 @@ def xpath(css):
assert xpath('e#myid') == (
"e[@id = 'myid']")
assert xpath('e:not(:nth-child(odd))') == (
"e[not((position() -1) mod 2 = 0 and position() >= 1)]")
"e[not((position() -1) mod 2 = 0)]")
assert xpath('e:nOT(*)') == (
"e[0]") # never matches
assert xpath('e f') == (
Expand Down Expand Up @@ -640,19 +657,25 @@ def pcss(main, *selectors, **kwargs):
assert pcss('li:nth-child(+2n+1)', 'li:nth-child(odd)') == [
'first-li', 'third-li', 'fifth-li', 'seventh-li']
assert pcss('li:nth-child(2n+4)') == ['fourth-li', 'sixth-li']
# FIXME: I'm not 100% sure this is right:
assert pcss('li:nth-child(3n+1)') == [
'first-li', 'fourth-li', 'seventh-li']
assert pcss('li:nth-last-child(0)') == [
'seventh-li']
assert pcss('li:nth-child(-n+3)') == [
'first-li', 'second-li', 'third-li']
assert pcss('li:nth-child(-2n+4)') == ['second-li', 'fourth-li']
assert pcss('li:nth-last-child(0)') == []
assert pcss('li:nth-last-child(1)') == ['seventh-li']
assert pcss('li:nth-last-child(2n)', 'li:nth-last-child(even)') == [
'second-li', 'fourth-li', 'sixth-li']
assert pcss('li:nth-last-child(2n+2)') == ['second-li', 'fourth-li']
assert pcss('li:nth-last-child(2n+1)') == [
'first-li', 'third-li', 'fifth-li', 'seventh-li']
assert pcss('li:nth-last-child(2n+2)') == [
'second-li', 'fourth-li', 'sixth-li']
assert pcss('li:nth-last-child(3n+1)') == [
'first-li', 'fourth-li', 'seventh-li']
assert pcss('ol:first-of-type') == ['first-ol']
assert pcss('ol:nth-child(1)') == []
assert pcss('ol:nth-of-type(2)') == ['second-ol']
# FIXME: like above', '(1) or (2)?
assert pcss('ol:nth-last-of-type(1)') == ['first-ol']
assert pcss('ol:nth-last-of-type(1)') == ['second-ol']
assert pcss('span:only-child') == ['foobar-span']
assert pcss('li div:only-child') == ['li-div']
assert pcss('div *:only-child') == ['li-div', 'foobar-span']
Expand Down