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Fix pond force unit definition #275

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Merged
apdavison merged 1 commit into from
Oct 14, 2026
Merged

Fix pond force unit definition #275

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7 changes: 7 additions & 0 deletions CHANGES.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,13 @@
CHANGES
=======

-----------
Unreleased
-----------

- Correct the pond force unit to 0.00980665 N (one gram-force); it was
previously 1000 times too large (`#44 <https://github.com/python-quantities/python-quantities/issues/44>`_).

------
0.16.4
------
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44 changes: 44 additions & 0 deletions quantities/tests/test_units.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import pytest

from .. import units as pq
from ..quantity import Quantity
from .common import TestCase


Expand Down Expand Up @@ -38,3 +39,46 @@ def test_code_injection(self):
with pytest.raises(LookupError) as exc_info:
pq.CompoundUnit("exec(\"print('Hello there.')\\nprint('General Wasabi!')\")")
assert "Wasabi" in str(exc_info.value)


class TestForceUnits(TestCase):

def test_pond_newtons(self):
# A pond is a gram-force, not a kilogram-force.
self.assertQuantityEqual(
pq.pond.rescale(pq.N), 0.00980665 * pq.N, delta=1e-12
)

def test_pond_names(self):
self.assertEqual(pq.pond.name, 'pond')
self.assertEqual(pq.pond.symbol, 'p')
for unit in ('pond', 'ponds', 'p'):
with self.subTest(unit=unit):
self.assertQuantityEqual(
Quantity(1, unit).rescale(pq.N),
0.00980665 * pq.N,
delta=1e-12
)

def test_pond_array(self):
self.assertQuantityEqual(
([-1, 0, 1, 1000] * pq.pond).rescale(pq.N),
[-0.00980665, 0, 0.00980665, 9.80665] * pq.N,
delta=1e-12
)

def test_pond_dimensionality(self):
self.assertEqual(
pq.pond.simplified.dimensionality,
(pq.kg * pq.m / pq.s**2).dimensionality
)

def test_gram_force_newtons(self):
self.assertQuantityEqual(
pq.gram_force.rescale(pq.N), 0.00980665 * pq.N, delta=1e-12
)

def test_kilogram_force_newtons(self):
self.assertQuantityEqual(
pq.kgf.rescale(pq.N), 9.80665 * pq.N, delta=1e-12
)
2 changes: 1 addition & 1 deletion quantities/units/force.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@
)
pond = UnitQuantity(
'pond',
g_0*kg,
g_0*gram,
symbol='p',
aliases=['ponds']
)
Expand Down
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