288 lines
8.6 KiB
Python
288 lines
8.6 KiB
Python
"""
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Utilities for interpreting CSS from Stylers for formatting non-HTML outputs.
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"""
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from __future__ import annotations
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import re
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import warnings
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class CSSWarning(UserWarning):
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"""
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This CSS syntax cannot currently be parsed.
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"""
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def _side_expander(prop_fmt: str):
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def expand(self, prop, value: str):
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tokens = value.split()
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try:
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mapping = self.SIDE_SHORTHANDS[len(tokens)]
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except KeyError:
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warnings.warn(f'Could not expand "{prop}: {value}"', CSSWarning)
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return
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for key, idx in zip(self.SIDES, mapping):
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yield prop_fmt.format(key), tokens[idx]
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return expand
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class CSSResolver:
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"""
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A callable for parsing and resolving CSS to atomic properties.
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"""
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UNIT_RATIOS = {
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"rem": ("pt", 12),
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"ex": ("em", 0.5),
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# 'ch':
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"px": ("pt", 0.75),
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"pc": ("pt", 12),
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"in": ("pt", 72),
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"cm": ("in", 1 / 2.54),
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"mm": ("in", 1 / 25.4),
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"q": ("mm", 0.25),
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"!!default": ("em", 0),
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}
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FONT_SIZE_RATIOS = UNIT_RATIOS.copy()
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FONT_SIZE_RATIOS.update(
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{
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"%": ("em", 0.01),
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"xx-small": ("rem", 0.5),
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"x-small": ("rem", 0.625),
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"small": ("rem", 0.8),
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"medium": ("rem", 1),
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"large": ("rem", 1.125),
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"x-large": ("rem", 1.5),
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"xx-large": ("rem", 2),
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"smaller": ("em", 1 / 1.2),
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"larger": ("em", 1.2),
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"!!default": ("em", 1),
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}
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)
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MARGIN_RATIOS = UNIT_RATIOS.copy()
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MARGIN_RATIOS.update({"none": ("pt", 0)})
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BORDER_WIDTH_RATIOS = UNIT_RATIOS.copy()
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BORDER_WIDTH_RATIOS.update(
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{
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"none": ("pt", 0),
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"thick": ("px", 4),
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"medium": ("px", 2),
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"thin": ("px", 1),
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# Default: medium only if solid
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}
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)
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SIDE_SHORTHANDS = {
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1: [0, 0, 0, 0],
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2: [0, 1, 0, 1],
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3: [0, 1, 2, 1],
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4: [0, 1, 2, 3],
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}
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SIDES = ("top", "right", "bottom", "left")
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def __call__(
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self,
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declarations_str: str,
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inherited: dict[str, str] | None = None,
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) -> dict[str, str]:
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"""
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The given declarations to atomic properties.
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Parameters
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----------
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declarations_str : str
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A list of CSS declarations
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inherited : dict, optional
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Atomic properties indicating the inherited style context in which
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declarations_str is to be resolved. ``inherited`` should already
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be resolved, i.e. valid output of this method.
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Returns
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-------
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dict
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Atomic CSS 2.2 properties.
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Examples
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--------
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>>> resolve = CSSResolver()
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>>> inherited = {'font-family': 'serif', 'font-weight': 'bold'}
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>>> out = resolve('''
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... border-color: BLUE RED;
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... font-size: 1em;
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... font-size: 2em;
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... font-weight: normal;
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... font-weight: inherit;
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... ''', inherited)
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>>> sorted(out.items()) # doctest: +NORMALIZE_WHITESPACE
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[('border-bottom-color', 'blue'),
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('border-left-color', 'red'),
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('border-right-color', 'red'),
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('border-top-color', 'blue'),
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('font-family', 'serif'),
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('font-size', '24pt'),
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('font-weight', 'bold')]
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"""
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props = dict(self.atomize(self.parse(declarations_str)))
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if inherited is None:
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inherited = {}
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props = self._update_initial(props, inherited)
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props = self._update_font_size(props, inherited)
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return self._update_other_units(props)
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def _update_initial(
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self,
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props: dict[str, str],
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inherited: dict[str, str],
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) -> dict[str, str]:
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# 1. resolve inherited, initial
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for prop, val in inherited.items():
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if prop not in props:
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props[prop] = val
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new_props = props.copy()
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for prop, val in props.items():
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if val == "inherit":
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val = inherited.get(prop, "initial")
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if val in ("initial", None):
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# we do not define a complete initial stylesheet
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del new_props[prop]
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else:
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new_props[prop] = val
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return new_props
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def _update_font_size(
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self,
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props: dict[str, str],
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inherited: dict[str, str],
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) -> dict[str, str]:
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# 2. resolve relative font size
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if props.get("font-size"):
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props["font-size"] = self.size_to_pt(
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props["font-size"],
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self._get_font_size(inherited),
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conversions=self.FONT_SIZE_RATIOS,
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)
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return props
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def _get_font_size(self, props: dict[str, str]) -> float | None:
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if props.get("font-size"):
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font_size_string = props["font-size"]
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return self._get_float_font_size_from_pt(font_size_string)
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return None
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def _get_float_font_size_from_pt(self, font_size_string: str) -> float:
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assert font_size_string.endswith("pt")
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return float(font_size_string.rstrip("pt"))
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def _update_other_units(self, props: dict[str, str]) -> dict[str, str]:
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font_size = self._get_font_size(props)
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# 3. TODO: resolve other font-relative units
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for side in self.SIDES:
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prop = f"border-{side}-width"
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if prop in props:
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props[prop] = self.size_to_pt(
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props[prop],
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em_pt=font_size,
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conversions=self.BORDER_WIDTH_RATIOS,
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)
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for prop in [f"margin-{side}", f"padding-{side}"]:
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if prop in props:
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# TODO: support %
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props[prop] = self.size_to_pt(
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props[prop],
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em_pt=font_size,
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conversions=self.MARGIN_RATIOS,
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)
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return props
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def size_to_pt(self, in_val, em_pt=None, conversions=UNIT_RATIOS):
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def _error():
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warnings.warn(f"Unhandled size: {repr(in_val)}", CSSWarning)
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return self.size_to_pt("1!!default", conversions=conversions)
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match = re.match(r"^(\S*?)([a-zA-Z%!].*)", in_val)
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if match is None:
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return _error()
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val, unit = match.groups()
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if val == "":
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# hack for 'large' etc.
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val = 1
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else:
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try:
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val = float(val)
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except ValueError:
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return _error()
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while unit != "pt":
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if unit == "em":
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if em_pt is None:
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unit = "rem"
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else:
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val *= em_pt
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unit = "pt"
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continue
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try:
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unit, mul = conversions[unit]
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except KeyError:
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return _error()
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val *= mul
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val = round(val, 5)
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if int(val) == val:
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size_fmt = f"{int(val):d}pt"
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else:
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size_fmt = f"{val:f}pt"
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return size_fmt
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def atomize(self, declarations):
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for prop, value in declarations:
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attr = "expand_" + prop.replace("-", "_")
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try:
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expand = getattr(self, attr)
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except AttributeError:
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yield prop, value
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else:
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for prop, value in expand(prop, value):
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yield prop, value
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expand_border_color = _side_expander("border-{:s}-color")
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expand_border_style = _side_expander("border-{:s}-style")
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expand_border_width = _side_expander("border-{:s}-width")
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expand_margin = _side_expander("margin-{:s}")
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expand_padding = _side_expander("padding-{:s}")
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def parse(self, declarations_str: str):
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"""
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Generates (prop, value) pairs from declarations.
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In a future version may generate parsed tokens from tinycss/tinycss2
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Parameters
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----------
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declarations_str : str
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"""
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for decl in declarations_str.split(";"):
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if not decl.strip():
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continue
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prop, sep, val = decl.partition(":")
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prop = prop.strip().lower()
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# TODO: don't lowercase case sensitive parts of values (strings)
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val = val.strip().lower()
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if sep:
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yield prop, val
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else:
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warnings.warn(
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f"Ill-formatted attribute: expected a colon in {repr(decl)}",
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CSSWarning,
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)
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