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