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Mutations are regular-expression-based replacements that are applied after variants have been computed. They are meant to be used for variations on character level. Add spelling variations for German umlauts.
57 lines
1.8 KiB
Python
57 lines
1.8 KiB
Python
# SPDX-License-Identifier: GPL-2.0-only
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#
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# This file is part of Nominatim. (https://nominatim.org)
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#
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# Copyright (C) 2022 by the Nominatim developer community.
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# For a full list of authors see the git log.
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"""
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Creator for mutation variants for the generic token analysis.
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"""
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import itertools
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import logging
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import re
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from nominatim.errors import UsageError
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LOG = logging.getLogger()
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def _zigzag(outer, inner):
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return itertools.chain.from_iterable(itertools.zip_longest(outer, inner, fillvalue=''))
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class MutationVariantGenerator:
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""" Generates name variants by applying a regular expression to the name
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and replacing it with one or more variants. When the regular expression
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matches more than once, each occurence is replaced with all replacement
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patterns.
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"""
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def __init__(self, pattern, replacements):
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self.pattern = re.compile(pattern)
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self.replacements = replacements
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if self.pattern.groups > 0:
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LOG.fatal("The mutation pattern %s contains a capturing group. "
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"This is not allowed.", pattern)
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raise UsageError("Bad mutation pattern in configuration.")
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def generate(self, names):
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""" Generator function for the name variants. 'names' is an iterable
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over a set of names for which the variants are to be generated.
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"""
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for name in names:
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parts = self.pattern.split(name)
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if len(parts) == 1:
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yield name
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else:
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for seps in self._fillers(len(parts)):
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yield ''.join(_zigzag(parts, seps))
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def _fillers(self, num_parts):
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""" Returns a generator for strings to join the given number of string
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parts in all possible combinations.
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"""
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return itertools.product(self.replacements, repeat=num_parts - 1)
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