Add rational exponent functionality to Units

setup.py

@@ -8,7 +8,7 @@
 
 setup(
     name="pyqn",
-    version="1.3.2",
+    version="1.4",
     description="A package for managing physical units and quantities",
     long_description=long_description,
     long_description_content_type="text/x-rst",
@@ -27,6 +27,8 @@
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
+        "Programming Language :: Python :: 3.11",
+        "Programming Language :: Python :: 3.12",
         "Programming Language :: Python :: 3 :: Only",
         "Operating System :: OS Independent",
     ],

src/pyqn/atom_unit.py

@@ -23,6 +23,7 @@
 # along with PyQn.  If not, see <http://www.gnu.org/licenses/>
 
 import sys
+from fractions import Fraction
 from pyparsing import Word, Group, Literal, Suppress, ParseException, oneOf, Optional
 from .si import si_prefixes
 from .base_unit import BaseUnit, base_unit_stems
@@ -33,13 +34,14 @@
 lowers = caps.lower()
 letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_0"
 digits = "123456789"
-exponent = Word(digits + "-")
+exponent = Word(digits + "-/")
 prefix = oneOf(list(si_prefixes.keys()))
 ustem = Word(letters + "Å" + "Ω")
 uatom = (Group("1" | (Optional(prefix) + ustem)) + Optional(exponent)) | (
     Group("1" | ustem) + Optional(exponent)
 )
 
+
 # floating point equality and its negation, to some suitable tolerance
 def feq(f1, f2, tol=1.0e-10):
     return abs(f1 - f2) <= tol
@@ -125,7 +127,10 @@ def parse(self, s_unit_atom):
         # if there is an exponent, determine what it is (default is 1)
         exponent = 1
         if len(uatom_data) == 2:
-            exponent = int(uatom_data[1])
+            if "/" in uatom_data:
+                exponent = int(uatom_data[1])
+            else:
+                exponent = Fraction(uatom_data[1])
         return AtomUnit(prefix, base_unit, exponent)
 
     def __pow__(self, power):

src/pyqn/units.py

@@ -20,6 +20,7 @@
 # You should have received a copy of the GNU General Public License
 # along with PyQn.  If not, see <http://www.gnu.org/licenses/>
 
+import re
 import copy
 from .dimensions import Dimensions
 from .dimensions import d_dimensionless, d_length, d_energy, d_time, d_temperature
@@ -82,18 +83,35 @@ def get_dims(self):
         return dims
 
     @classmethod
-    def parse(self, s_compoundunit):
+    def parse(self, s_compoundunit, no_divided_units=False):
         """
         Parse the string s_compoundunit and return the corresponding
         Units object.
 
         """
 
+        if no_divided_units:
+            # s_compoundunit does not consist of any units separated by '/'
+            # so parse immediately as a sequence of multiplied units.
+            return Units.parse_mult_units(s_compoundunit)
+
+        # We need to temporarily identify rational exponents (e.g. "Pa-1/2")
+        # and replace the / with : so that we can split up the atomic units
+        # properly.
+        patt = r"\d+/\d+"
+        rational_exponents = re.findall(patt, s_compoundunit)
+        for e in rational_exponents:
+            es = e.replace("/", ":")
+            s_compoundunit = s_compoundunit.replace(e, es)
+
         div_fields = s_compoundunit.split("/")
-        ndiv_fields = len(div_fields)
-        compound_unit = Units.parse_mult_units(div_fields[0])
+        # don't forget to put back the "/" character in any rational exponents.
+        compound_unit = Units.parse_mult_units(div_fields[0].replace(":", "/"))
         for div_field in div_fields[1:]:
-            compound_unit = compound_unit / Units.parse(div_field)
+            div_field = div_field.replace(":", "/")
+            compound_unit = compound_unit / Units.parse(
+                div_field, no_divided_units=True
+            )
         return compound_unit
 
     @classmethod
@@ -244,7 +262,7 @@ def html(self):
         for i, atom_unit in enumerate(self.atom_units):
             h.extend([atom_unit.prefix or "", atom_unit.base_unit.stem])
             if atom_unit.exponent != 1:
-                h.append("<sup>{:d}</sup>".format(atom_unit.exponent))
+                h.append(f"<sup>{atom_unit.exponent}</sup>")
             if i < n - 1:
                 h.append(" ")
         return "".join(h)

tests/test_conversions.py

@@ -52,6 +52,15 @@ def test_spec_conversions(self):
         self.assertAlmostEqual(u1.conversion(u2, force="spec"), 5.0341165675427096e22)
         self.assertAlmostEqual(u1.conversion(u3, force="spec"), 1.5091901796421518e33)
 
+    def test_rational_units_conversion(self):
+        u1 = Units("Hz-1/2")
+        u2 = Units("ns1/2")
+        self.assertAlmostEqual(u1.conversion(u2), 10**4.5)
+
+        u3 = Units("m-3/2")
+        u4 = Units("inch-3/2")
+        self.assertAlmostEqual(u3.conversion(u4), 0.0254**1.5)
+
 
 if __name__ == "__main__":
     unittest.main()

tests/test_units.py

@@ -6,6 +6,7 @@
 # Unit tests for the Units class.
 
 import unittest
+from fractions import Fraction
 from pyqn.units import Units
 from pyqn.dimensions import Dimensions, d_energy
 
@@ -107,6 +108,34 @@ def test_html(self):
         u2 = Units("μs.J/m3")
         self.assertEqual(u2.html, "μs J m<sup>-3</sup>")
 
+    def test_units_with_rational_powers(self):
+        u1 = Units("m-3.Pa-1/2")
+        u2 = Units("cm-3.bar-1/2")
+        self.assertEqual(str(u1), "m-3.Pa-1/2")
+        self.assertEqual(u1.dims, u2.dims)
+        self.assertEqual(u1.html, "m<sup>-3</sup> Pa<sup>-1/2</sup>")
+
+        self.assertEqual(u1.dims, Dimensions(M=-0.5, T=1, L=-2.5))
+
+        u3 = Units("kg1/2.m-3/2")
+        self.assertEqual(str(u3), "kg1/2.m-3/2")
+        self.assertEqual(u3.html, "kg<sup>1/2</sup> m<sup>-3/2</sup>")
+
+    def test_rational_units_algebra(self):
+        u1 = Units("m-3.Pa-1/2")
+        u2 = Units("m3")
+        u3 = u1 * u2
+        self.assertEqual(str(u3), "Pa-1/2")
+
+        u4 = Units("Pa-2/3.s4")
+        u5 = u1 / u4
+        u6 = Units("m-3.s4.Pa1/6")
+        self.assertEqual(str(u6), "m-3.s4.Pa1/6")
+        self.assertEqual(
+            u6.dims,
+            Dimensions(M=Fraction("1/6"), T=Fraction("11/3"), L=Fraction("-19/6")),
+        )
+
 
 if __name__ == "__main__":
     unittest.main()