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112 lines
4.3 KiB
Python
112 lines
4.3 KiB
Python
"""
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A module for parsing and generating `fontconfig patterns`_.
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.. _fontconfig patterns:
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https://www.freedesktop.org/software/fontconfig/fontconfig-user.html
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"""
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# This class logically belongs in `matplotlib.font_manager`, but placing it
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# there would have created cyclical dependency problems, because it also needs
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# to be available from `matplotlib.rcsetup` (for parsing matplotlibrc files).
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from functools import lru_cache, partial
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import re
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from pyparsing import (
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Group, Optional, ParseException, Regex, StringEnd, Suppress, ZeroOrMore, one_of)
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_family_punc = r'\\\-:,'
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_family_unescape = partial(re.compile(r'\\(?=[%s])' % _family_punc).sub, '')
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_family_escape = partial(re.compile(r'(?=[%s])' % _family_punc).sub, r'\\')
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_value_punc = r'\\=_:,'
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_value_unescape = partial(re.compile(r'\\(?=[%s])' % _value_punc).sub, '')
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_value_escape = partial(re.compile(r'(?=[%s])' % _value_punc).sub, r'\\')
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_CONSTANTS = {
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'thin': ('weight', 'light'),
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'extralight': ('weight', 'light'),
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'ultralight': ('weight', 'light'),
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'light': ('weight', 'light'),
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'book': ('weight', 'book'),
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'regular': ('weight', 'regular'),
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'normal': ('weight', 'normal'),
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'medium': ('weight', 'medium'),
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'demibold': ('weight', 'demibold'),
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'semibold': ('weight', 'semibold'),
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'bold': ('weight', 'bold'),
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'extrabold': ('weight', 'extra bold'),
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'black': ('weight', 'black'),
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'heavy': ('weight', 'heavy'),
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'roman': ('slant', 'normal'),
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'italic': ('slant', 'italic'),
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'oblique': ('slant', 'oblique'),
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'ultracondensed': ('width', 'ultra-condensed'),
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'extracondensed': ('width', 'extra-condensed'),
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'condensed': ('width', 'condensed'),
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'semicondensed': ('width', 'semi-condensed'),
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'expanded': ('width', 'expanded'),
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'extraexpanded': ('width', 'extra-expanded'),
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'ultraexpanded': ('width', 'ultra-expanded'),
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}
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@lru_cache # The parser instance is a singleton.
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def _make_fontconfig_parser():
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def comma_separated(elem):
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return elem + ZeroOrMore(Suppress(",") + elem)
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family = Regex(fr"([^{_family_punc}]|(\\[{_family_punc}]))*")
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size = Regex(r"([0-9]+\.?[0-9]*|\.[0-9]+)")
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name = Regex(r"[a-z]+")
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value = Regex(fr"([^{_value_punc}]|(\\[{_value_punc}]))*")
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prop = Group((name + Suppress("=") + comma_separated(value)) | one_of(_CONSTANTS))
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return (
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Optional(comma_separated(family)("families"))
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+ Optional("-" + comma_separated(size)("sizes"))
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+ ZeroOrMore(":" + prop("properties*"))
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+ StringEnd()
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)
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# `parse_fontconfig_pattern` is a bottleneck during the tests because it is
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# repeatedly called when the rcParams are reset (to validate the default
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# fonts). In practice, the cache size doesn't grow beyond a few dozen entries
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# during the test suite.
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@lru_cache
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def parse_fontconfig_pattern(pattern):
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"""
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Parse a fontconfig *pattern* into a dict that can initialize a
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`.font_manager.FontProperties` object.
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"""
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parser = _make_fontconfig_parser()
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try:
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parse = parser.parse_string(pattern)
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except ParseException as err:
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# explain becomes a plain method on pyparsing 3 (err.explain(0)).
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raise ValueError("\n" + ParseException.explain(err, 0)) from None
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parser.reset_cache()
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props = {}
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if "families" in parse:
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props["family"] = [*map(_family_unescape, parse["families"])]
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if "sizes" in parse:
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props["size"] = [*parse["sizes"]]
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for prop in parse.get("properties", []):
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if len(prop) == 1:
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prop = _CONSTANTS[prop[0]]
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k, *v = prop
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props.setdefault(k, []).extend(map(_value_unescape, v))
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return props
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def generate_fontconfig_pattern(d):
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"""Convert a `.FontProperties` to a fontconfig pattern string."""
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kvs = [(k, getattr(d, f"get_{k}")())
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for k in ["style", "variant", "weight", "stretch", "file", "size"]]
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# Families is given first without a leading keyword. Other entries (which
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# are necessarily scalar) are given as key=value, skipping Nones.
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return (",".join(_family_escape(f) for f in d.get_family())
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+ "".join(f":{k}={_value_escape(str(v))}"
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for k, v in kvs if v is not None))
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