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+# SPDX-License-Identifier: AGPL-3.0-or-later
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+"""Unit conversion on the basis of `SPARQL/WIKIDATA Precision, Units and
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+Coordinates`_
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+
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+.. _SPARQL/WIKIDATA Precision, Units and Coordinates:
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+ https://en.wikibooks.org/wiki/SPARQL/WIKIDATA_Precision,_Units_and_Coordinates#Quantities
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+"""
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+
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+__all__ = ["convert_from_si", "convert_to_si", "symbol_to_si"]
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+
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+import collections
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+
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+from searx import data
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+from searx.engines import wikidata
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+
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+ADDITIONAL_UNITS = [
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+ {
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+ "si_name": "Q11579",
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+ "symbol": "°C",
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+ "to_si": lambda val: val + 273.15,
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+ "from_si": lambda val: val - 273.15,
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+ },
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+ {
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+ "si_name": "Q11579",
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+ "symbol": "°F",
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+ "to_si": lambda val: (val + 459.67) * 5 / 9,
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+ "from_si": lambda val: (val * 9 / 5) - 459.67,
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+ },
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+]
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+"""Additional items to convert from a measure unit to a SI unit (vice versa).
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+
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+.. code:: python
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+
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+ {
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+ "si_name": "Q11579", # Wikidata item ID of the SI unit (Kelvin)
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+ "symbol": "°C", # symbol of the measure unit
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+ "to_si": lambda val: val + 273.15, # convert measure value (val) to SI unit
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+ "from_si": lambda val: val - 273.15, # convert SI value (val) measure unit
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+ },
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+ {
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+ "si_name": "Q11573",
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+ "symbol": "mi",
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+ "to_si": 1609.344, # convert measure value (val) to SI unit
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+ "from_si": 1 / 1609.344 # convert SI value (val) measure unit
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+ },
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+
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+The values of ``to_si`` and ``from_si`` can be of :py:obj:`float` (a multiplier)
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+or a callable_ (val in / converted value returned).
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+
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+.. _callable: https://docs.python.org/3/glossary.html#term-callable
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+"""
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+
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+
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+ALIAS_SYMBOLS = {
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+ '°C': ('C',),
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+ '°F': ('F',),
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+ 'mi': ('L',),
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+}
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+"""Alias symbols for known unit of measure symbols / by example::
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+
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+ '°C': ('C', ...), # list of alias symbols for °C (Q69362731)
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+ '°F': ('F', ...), # list of alias symbols for °F (Q99490479)
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+ 'mi': ('L',), # list of alias symbols for mi (Q253276)
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+"""
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+
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+
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+SYMBOL_TO_SI = []
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+UNITS_BY_SI_NAME: dict | None = None
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+
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+
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+def convert_from_si(si_name: str, symbol: str, value: float | int) -> float:
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+ from_si = units_by_si_name(si_name)[symbol][symbol]["from_si"]
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+ if isinstance(from_si, (float, int)):
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+ value = float(value) * from_si
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+ else:
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+ value = from_si(float(value))
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+ return value
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+
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+
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+def convert_to_si(si_name: str, symbol: str, value: float | int) -> float:
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+ to_si = units_by_si_name(si_name)[symbol][symbol]["to_si"]
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+ if isinstance(to_si, (float, int)):
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+ value = float(value) * to_si
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+ else:
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+ value = to_si(float(value))
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+ return value
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+
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+
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+def units_by_si_name(si_name):
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+
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+ global UNITS_BY_SI_NAME
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+ if UNITS_BY_SI_NAME is not None:
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+ return UNITS_BY_SI_NAME[si_name]
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+
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+ UNITS_BY_SI_NAME = {}
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+ for item in symbol_to_si():
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+ by_symbol = UNITS_BY_SI_NAME.get(si_name)
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+ if by_symbol is None:
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+ by_symbol = {}
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+ UNITS_BY_SI_NAME[si_name] = by_symbol
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+ by_symbol[item["symbol"]] = item
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+ return UNITS_BY_SI_NAME[si_name]
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+
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+
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+def symbol_to_si():
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+ """Generates a list of tuples, each tuple is a measure unit and the fields
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+ in the tuple are:
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+
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+ 0. Symbol of the measure unit (e.g. 'mi' for measure unit 'miles' Q253276)
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+
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+ 1. SI name of the measure unit (e.g. Q11573 for SI unit 'metre')
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+
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+ 2. Factor to get SI value from measure unit (e.g. 1mi is equal to SI 1m
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+ multiplied by 1609.344)
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+
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+ 3. Factor to get measure value from from SI value (e.g. SI 100m is equal to
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+ 100mi divided by 1609.344)
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+
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+ The returned list is sorted, the first items are created from
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+ ``WIKIDATA_UNITS``, the second group of items is build from
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+ :py:obj:`ADDITIONAL_UNITS` and items created from :py:obj:`ALIAS_SYMBOLS`.
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+
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+ If you search this list for a symbol, then a match with a symbol from
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+ Wikidata has the highest weighting (first hit in the list), followed by the
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+ symbols from the :py:obj:`ADDITIONAL_UNITS` and the lowest weighting is
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+ given to the symbols resulting from the aliases :py:obj:`ALIAS_SYMBOLS`.
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+
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+ """
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+
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+ global SYMBOL_TO_SI # pylint: disable=global-statement
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+ if SYMBOL_TO_SI:
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+ return SYMBOL_TO_SI
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+
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+ # filter out units which can't be normalized to a SI unit and filter out
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+ # units without a symbol / arcsecond does not have a symbol
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+ # https://www.wikidata.org/wiki/Q829073
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+
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+ for item in data.WIKIDATA_UNITS.values():
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+ if item['to_si_factor'] and item['symbol']:
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+ SYMBOL_TO_SI.append(
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+ (
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+ item['symbol'],
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+ item['si_name'],
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+ 1 / item['to_si_factor'], # from_si
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+ item['to_si_factor'], # to_si
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+ item['symbol'],
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+ )
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+ )
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+
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+ for item in ADDITIONAL_UNITS:
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+ SYMBOL_TO_SI.append(
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+ (
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+ item['symbol'],
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+ item['si_name'],
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+ item['from_si'],
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+ item['to_si'],
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+ item['symbol'],
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+ )
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+ )
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+
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+ alias_items = []
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+ for item in SYMBOL_TO_SI:
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+ for alias in ALIAS_SYMBOLS.get(item[0], ()):
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+ alias_items.append(
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+ (
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+ alias,
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+ item[1],
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+ item[2], # from_si
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+ item[3], # to_si
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+ item[0], # origin unit
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+ )
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+ )
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+ SYMBOL_TO_SI = SYMBOL_TO_SI + alias_items
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+ return SYMBOL_TO_SI
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+
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+
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+# the response contains duplicate ?item with the different ?symbol
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+# "ORDER BY ?item DESC(?rank) ?symbol" provides a deterministic result
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+# even if a ?item has different ?symbol of the same rank.
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+# A deterministic result
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+# see:
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+# * https://www.wikidata.org/wiki/Help:Ranking
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+# * https://www.mediawiki.org/wiki/Wikibase/Indexing/RDF_Dump_Format ("Statement representation" section)
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+# * https://w.wiki/32BT
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+# * https://en.wikibooks.org/wiki/SPARQL/WIKIDATA_Precision,_Units_and_Coordinates#Quantities
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+# see the result for https://www.wikidata.org/wiki/Q11582
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+# there are multiple symbols the same rank
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+
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+SARQL_REQUEST = """
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+SELECT DISTINCT ?item ?symbol ?tosi ?tosiUnit
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+WHERE
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+{
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+ ?item wdt:P31/wdt:P279 wd:Q47574 .
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+ ?item p:P5061 ?symbolP .
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+ ?symbolP ps:P5061 ?symbol ;
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+ wikibase:rank ?rank .
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+ OPTIONAL {
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+ ?item p:P2370 ?tosistmt .
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+ ?tosistmt psv:P2370 ?tosinode .
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+ ?tosinode wikibase:quantityAmount ?tosi .
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+ ?tosinode wikibase:quantityUnit ?tosiUnit .
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+ }
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+ FILTER(LANG(?symbol) = "en").
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+}
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+ORDER BY ?item DESC(?rank) ?symbol
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+"""
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+
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+
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+def fetch_units():
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+ """Fetch units from Wikidata. Function is used to update persistence of
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+ :py:obj:`searx.data.WIKIDATA_UNITS`."""
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+
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+ results = collections.OrderedDict()
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+ response = wikidata.send_wikidata_query(SARQL_REQUEST)
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+ for unit in response['results']['bindings']:
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+
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+ symbol = unit['symbol']['value']
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+ name = unit['item']['value'].rsplit('/', 1)[1]
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+ si_name = unit.get('tosiUnit', {}).get('value', '')
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+ if si_name:
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+ si_name = si_name.rsplit('/', 1)[1]
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+
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+ to_si_factor = unit.get('tosi', {}).get('value', '')
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+ if name not in results:
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+ # ignore duplicate: always use the first one
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+ results[name] = {
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+ 'symbol': symbol,
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+ 'si_name': si_name if si_name else None,
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+ 'to_si_factor': float(to_si_factor) if to_si_factor else None,
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+ }
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+ return results
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Markus Heiser