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import re
from .parser import _next_significant, _to_token_iterator
def parse_nth(input):
"""Parse `<An+B> <https://drafts.csswg.org/css-syntax-3/#anb>`_,
as found in `:nth-child()
<https://drafts.csswg.org/selectors/#nth-child-pseudo>`_
and related Selector pseudo-classes.
Although tinycss2 does not include a full Selector parser,
this bit of syntax is included as it is particularly tricky to define
on top of a CSS tokenizer.
:type input: :obj:`str` or :term:`iterable`
:param input: A string or an iterable of :term:`component values`.
:returns:
A ``(a, b)`` tuple of integers, or :obj:`None` if the input is invalid.
"""
tokens = _to_token_iterator(input, skip_comments=True)
token = _next_significant(tokens)
if token is None:
return
token_type = token.type
if token_type == 'number' and token.is_integer:
return parse_end(tokens, 0, token.int_value)
elif token_type == 'dimension' and token.is_integer:
unit = token.lower_unit
if unit == 'n':
return parse_b(tokens, token.int_value)
elif unit == 'n-':
return parse_signless_b(tokens, token.int_value, -1)
else:
match = N_DASH_DIGITS_RE.match(unit)
if match:
return parse_end(tokens, token.int_value, int(match.group(1)))
elif token_type == 'ident':
ident = token.lower_value
if ident == 'even':
return parse_end(tokens, 2, 0)
elif ident == 'odd':
return parse_end(tokens, 2, 1)
elif ident == 'n':
return parse_b(tokens, 1)
elif ident == '-n':
return parse_b(tokens, -1)
elif ident == 'n-':
return parse_signless_b(tokens, 1, -1)
elif ident == '-n-':
return parse_signless_b(tokens, -1, -1)
elif ident[0] == '-':
match = N_DASH_DIGITS_RE.match(ident[1:])
if match:
return parse_end(tokens, -1, int(match.group(1)))
else:
match = N_DASH_DIGITS_RE.match(ident)
if match:
return parse_end(tokens, 1, int(match.group(1)))
elif token == '+':
token = next(tokens) # Whitespace after an initial '+' is invalid.
if token.type == 'ident':
ident = token.lower_value
if ident == 'n':
return parse_b(tokens, 1)
elif ident == 'n-':
return parse_signless_b(tokens, 1, -1)
else:
match = N_DASH_DIGITS_RE.match(ident)
if match:
return parse_end(tokens, 1, int(match.group(1)))
def parse_b(tokens, a):
token = _next_significant(tokens)
if token is None:
return (a, 0)
elif token == '+':
return parse_signless_b(tokens, a, 1)
elif token == '-':
return parse_signless_b(tokens, a, -1)
elif (token.type == 'number' and token.is_integer and
token.representation[0] in '-+'):
return parse_end(tokens, a, token.int_value)
def parse_signless_b(tokens, a, b_sign):
token = _next_significant(tokens)
if (token.type == 'number' and token.is_integer and
token.representation[0] not in '-+'):
return parse_end(tokens, a, b_sign * token.int_value)
def parse_end(tokens, a, b):
if _next_significant(tokens) is None:
return (a, b)
N_DASH_DIGITS_RE = re.compile('^n(-[0-9]+)$')
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