251 lines
7.8 KiB
Python
251 lines
7.8 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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import re
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import warnings
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class CSSWarning(UserWarning):
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"""This CSS syntax cannot currently be parsed"""
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pass
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class CSSResolver(object):
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"""A callable for parsing and resolving CSS to atomic properties
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"""
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INITIAL_STYLE = {
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}
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def __call__(self, declarations_str, inherited=None):
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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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props : 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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# 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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for prop, val in list(props.items()):
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if val == 'inherit':
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val = inherited.get(prop, 'initial')
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if val == 'initial':
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val = self.INITIAL_STYLE.get(prop)
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if val is None:
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# we do not define a complete initial stylesheet
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del props[prop]
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else:
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props[prop] = val
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# 2. resolve relative font size
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if props.get('font-size'):
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if 'font-size' in inherited:
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em_pt = inherited['font-size']
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assert em_pt[-2:] == 'pt'
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em_pt = float(em_pt[:-2])
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else:
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em_pt = None
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props['font-size'] = self.size_to_pt(
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props['font-size'], em_pt, conversions=self.FONT_SIZE_RATIOS)
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font_size = float(props['font-size'][:-2])
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else:
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font_size = None
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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 = 'border-{side}-width'.format(side=side)
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if prop in props:
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props[prop] = self.size_to_pt(
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props[prop], em_pt=font_size,
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conversions=self.BORDER_WIDTH_RATIOS)
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for prop in ['margin-{side}'.format(side=side),
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'padding-{side}'.format(side=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], em_pt=font_size,
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conversions=self.MARGIN_RATIOS)
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return props
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UNIT_RATIOS = {
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'rem': ('pt', 12),
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'ex': ('em', .5),
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# 'ch':
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'px': ('pt', .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', .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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'%': ('em', .01),
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'xx-small': ('rem', .5),
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'x-small': ('rem', .625),
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'small': ('rem', .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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MARGIN_RATIOS = UNIT_RATIOS.copy()
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MARGIN_RATIOS.update({
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'none': ('pt', 0),
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})
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BORDER_WIDTH_RATIOS = UNIT_RATIOS.copy()
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BORDER_WIDTH_RATIOS.update({
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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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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('Unhandled size: {val!r}'.format(val=in_val),
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CSSWarning)
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return self.size_to_pt('1!!default', conversions=conversions)
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try:
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val, unit = re.match(r'^(\S*?)([a-zA-Z%!].*)', in_val).groups()
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except AttributeError:
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return _error()
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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 = '{fmt:d}pt'.format(fmt=int(val))
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else:
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size_fmt = '{fmt:f}pt'.format(fmt=val)
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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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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 _side_expander(prop_fmt):
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def expand(self, prop, value):
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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('Could not expand "{prop}: {val}"'
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.format(prop=prop, val=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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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):
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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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"""
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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('Ill-formatted attribute: expected a colon '
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'in {decl!r}'.format(decl=decl), CSSWarning)
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