Upgrade pint==0.19.1 (#415)

Upgrade pint, which now uses h to denote hours instead of Planck's constant (making my workaround redundant). Also prefer shorter units as a general rule. * Upgrade pint to 0.19 in which h is the symbol for hour rather than Planck's constant Signed-off-by: F.N. Claessen <felix@seita.nl> * Simplify setup of unit registry Signed-off-by: F.N. Claessen <felix@seita.nl> * Add currencies to list of preferred units Signed-off-by: F.N. Claessen <felix@seita.nl> * Always prefer shorter units Signed-off-by: F.N. Claessen <felix@seita.nl> * Add todo to take into account magnitude when deciding what the shortest unit is (requires decimal registry) Signed-off-by: F.N. Claessen <felix@seita.nl> * Add todo to switch to decimal unit registry Signed-off-by: F.N. Claessen <felix@seita.nl> * Add module docstring Signed-off-by: F.N. Claessen <felix@seita.nl> * Changelog entry Signed-off-by: F.N. Claessen <felix@seita.nl>
FlexMeasures · Apr 9, 2022 · 559eccd · 559eccd
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diff --git a/documentation/changelog.rst b/documentation/changelog.rst
@@ -15,6 +15,7 @@ Bugfixes
 
 Infrastructure / Support
 ----------------------
+* Unit conversion prefers shorter units in general [see `PR #415 <http://www.github.com/FlexMeasures/flexmeasures/pull/415>`_]
 
 
 v0.9.2 | April XX, 2022

diff --git a/flexmeasures/utils/tests/test_unit_utils.py b/flexmeasures/utils/tests/test_unit_utils.py
@@ -70,7 +70,7 @@ def test_convert_unit(
         ("m³", None, "m³/h"),
         ("kWh", None, "kW"),
         ("km", "h", "km/h"),
-        ("m", "s", "km/h"),
+        ("m", "s", "m/s"),
     ],
 )
 def test_determine_flow_unit(
@@ -88,6 +88,8 @@ def test_determine_flow_unit(
     "unit, time_unit, expected_unit",
     [
         ("m³/h", None, "m³"),
+        ("km³/h", None, "km³"),
+        # ("hm³/h", None, "hm³"),  # todo: uncomment after switching to decimal unit registry
         ("kW", None, "kWh"),
         ("m/s", "s", "m"),
         ("m/s", "h", "km"),

diff --git a/flexmeasures/utils/unit_utils.py b/flexmeasures/utils/unit_utils.py
@@ -1,44 +1,36 @@
+"""Utility module for unit conversion
+
+FlexMeasures stores units as strings in short scientific notation (such as 'kWh' to denote kilowatt-hour).
+We use the pint library to convert data between compatible units (such as 'm/s' to 'km/h').
+Three-letter currency codes (such as 'KRW' to denote South Korean Won) are valid units.
+Note that converting between currencies requires setting up a sensor that registers conversion rates over time.
+The preferred compact form for combinations of units can be derived automatically (such as 'kW*EUR/MWh' to 'EUR/h').
+Time series with fixed resolution can be converted from units of flow to units of stock (such as 'kW' to 'kWh'), and vice versa.
+Percentages can be converted to units of some physical capacity if a capacity is known (such as '%' to 'kWh').
+"""
+
 from datetime import timedelta
 from typing import List, Optional, Union
 
 from moneyed import list_all_currencies
-import importlib.resources as pkg_resources
 import numpy as np
 import pandas as pd
 import pint
 import timely_beliefs as tb
 
-# Edit constants template to stop using h to represent planck_constant
-constants_template = (
-    pkg_resources.read_text(pint, "constants_en.txt")
-    .replace("= h  ", "     ")
-    .replace(" h ", " planck_constant ")
-)
-
-# Edit units template to use h to represent hour instead of planck_constant
-units_template = (
-    pkg_resources.read_text(pint, "default_en.txt")
-    .replace("@import constants_en.txt", "")
-    .replace(" h ", " planck_constant ")
-    .replace("hour = 60 * minute = hr", "hour = 60 * minute = h = hr")
-)
 
 # Create custom template
 custom_template = [f"{c} = [currency_{c}]" for c in list_all_currencies()]
 
-# Join templates as iterable object
-full_template = (
-    constants_template.split("\n") + units_template.split("\n") + custom_template
-)
-
 # Set up UnitRegistry with abbreviated scientific format
 ur = pint.UnitRegistry(
-    full_template,
+    # non_int_type=decimal.Decimal,  # todo: switch to decimal unit registry, after https://github.com/hgrecco/pint/issues/1505
     preprocessors=[
         lambda s: s.replace("%", " percent "),
         lambda s: s.replace("‰", " permille "),
     ],
 )
+ur.load_definitions(custom_template)
 ur.default_format = "~P"  # short pretty
 ur.define("percent = 1 / 100 = %")
 ur.define("permille = 1 / 1000 = ‰")
@@ -57,6 +49,8 @@
     "V",
     "A",
     "dimensionless",
+] + [
+    str(c) for c in list_all_currencies()
 ]  # todo: move to config setting, with these as a default (NB prefixes do not matter here, this is about SI base units, so km/h is equivalent to m/h)
 PREFERRED_UNITS_DICT = dict(
     [(ur.parse_expression(x).dimensionality, x) for x in PREFERRED_UNITS]
@@ -67,7 +61,16 @@ def to_preferred(x: pint.Quantity) -> pint.Quantity:
     """From https://github.com/hgrecco/pint/issues/676#issuecomment-689157693"""
     dim = x.dimensionality
     if dim in PREFERRED_UNITS_DICT:
-        return x.to(PREFERRED_UNITS_DICT[dim]).to_compact()
+
+        compact_unit = x.to(PREFERRED_UNITS_DICT[dim]).to_compact()
+
+        # todo: switch to decimal unit registry and then swap out the if statements below
+        # if len(f"{compact_unit.magnitude}" + "{:~P}".format(compact_unit.units)) < len(
+        #     f"{x.magnitude}" + "{:~P}".format(x.units)
+        # ):
+        #     return compact_unit
+        if len("{:~P}".format(compact_unit.units)) < len("{:~P}".format(x.units)):
+            return compact_unit
     return x
 
 
@@ -126,11 +129,8 @@ def determine_stock_unit(flow_unit: str, time_unit: str = "h"):
     >>> determine_stock_unit("m³/h")  # m³
     >>> determine_stock_unit("kW")  # kWh
     """
-    stock = ur.Quantity(flow_unit) * ur.Quantity(time_unit)
-    return min(
-        ["{:~P}".format(stock.units), "{:~P}".format(to_preferred(stock).units)],
-        key=len,
-    )
+    stock = to_preferred(ur.Quantity(flow_unit) * ur.Quantity(time_unit))
+    return "{:~P}".format(stock.units)
 
 
 def units_are_convertible(

diff --git a/requirements/app.in b/requirements/app.in
@@ -6,7 +6,7 @@ pscript
 pandas
 # pandas-bokeh 0.5 requires bokeh>=2.0, but bokeh still doesn't support sharing a legend across plots
 pandas-bokeh==0.4.3
-pint
+pint>=0.19.1
 py-moneyed
 iso8601
 xlrd

diff --git a/requirements/app.txt b/requirements/app.txt
@@ -241,7 +241,7 @@ pillow==9.0.1
     # via
     #   bokeh
     #   matplotlib
-pint==0.18
+pint==0.19.1
     # via -r requirements/app.in
 ply==3.11
     # via pyomo