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Delayed import of pyparsing for fontconfig pattern matching #12915

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Delayed import of pyparsing for fontconfig pattern matching #12915

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37 changes: 34 additions & 3 deletions lib/matplotlib/fontconfig_pattern.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,8 +12,6 @@
from functools import lru_cache
import re
import numpy as np
from pyparsing import (Literal, ZeroOrMore, Optional, Regex, StringEnd,
ParseException, Suppress)

family_punc = r'\\\-:,'
family_unescape = re.compile(r'\\([%s])' % family_punc).sub
Expand All @@ -23,6 +21,14 @@
value_unescape = re.compile(r'\\([%s])' % value_punc).sub
value_escape = re.compile(r'([%s])' % value_punc).sub

_SIMPLE_PATTERN_CACHE = {
'cursive': {'family': ['cursive']},
'sans': {'family': ['sans']},
'monospace': {'family': ['monospace']},
'sans:italic': {'family': ['sans'], 'slant': ['italic']},
'sans:bold': {'family': ['sans'], 'weight': ['bold']},
}


class FontconfigPatternParser:
"""
Expand Down Expand Up @@ -60,6 +66,9 @@ class FontconfigPatternParser:
}

def __init__(self):
# delayed import. Only executed when needed
from pyparsing import (Literal, ZeroOrMore, Optional, Regex, StringEnd,
ParseException, Suppress)

family = Regex(
r'([^%s]|(\\[%s]))*' % (family_punc, family_punc)
Expand Down Expand Up @@ -167,11 +176,33 @@ def _property(self, s, loc, tokens):
return []


@lru_cache(maxsize=1)
def _get_parser():
"""Return a cached FontconfigPatternParser instance."""
return FontconfigPatternParser()


# `parse_fontconfig_pattern` is a bottleneck during the tests because it is
# repeatedly called when the rcParams are reset (to validate the default
# fonts). In practice, the cache size doesn't grow beyond a few dozen entries
# during the test suite.
parse_fontconfig_pattern = lru_cache()(FontconfigPatternParser().parse)
@lru_cache()
def parse_fontconfig_pattern(pattern):
"""
Parse the given fontconfig *pattern* and return a dictionary
of key/value pairs useful for initializing a
:class:`font_manager.FontProperties` object.
"""

# Try a lookup on simple patterns first. This can prevent the need to
# create a full parser and to import pyparsing. If only patterns from
# _SIMPLE_PATTERN_CACHE are used in the matplotlibrc file, this will
# speed up the import of matplotlib.
parsed = _SIMPLE_PATTERN_CACHE.get(pattern)
if parsed is not None:
return parsed

return _get_parser().parse(pattern)


def _escape_val(val, escape_func):
Expand Down