Implement an 'undef' Units functionality

README.rst

@@ -10,59 +10,3 @@ transforming physical quantities and their units.
 Units are specified as strings using a simple and flexible syntax,
 and may be compared, output in different formats and manipulated using a
 variety of predefined Python methods.
-
-
-
-Installation:
-=============
-
-The PyQn package can be installed either from PyPI_ using pip
-
-.. code-block:: bash
-
-    python3 -m pip install pyqn
-
-or from the source by running (one of the two) from the project source directory.
-
-.. code-block:: bash
-
-    # either
-    python setup.py install
-
-    # or
-    python3 -m pip install .
-
-
-
-Examples:
-=========
-
-Units
------
-The units of physical quantities are represented by the ``Units`` class. A
-``Units`` object is instantiated from a valid units string and supports ions,
-isotopologues, as well as a few special species. This object contains
-attributes including the dimensions, HTML and LaTeX representations, and
-methods for conversion to different compatible units.
-
-.. code-block:: pycon
-
-    >>> from pyqn.units import Units
-    >>> u1 = Units('km')
-
-    >>> u2 = Units('hr')
-
-    >>> u3 = u1/u2
-
-    >>> print(u3)
-    km.hr-1
-
-    >>> u4 = Units('m/s')
-
-    >>> u3.conversion(u4)        # OK: can convert from km/hr to m/s
-    Out[7]: 0.2777777777777778
-
-    >>> u3.conversion(u2)        #  Oops: can't convert from km/hr to m!
-    ...
-    UnitsError: Failure in units conversion: units km.hr-1[L.T-1] and hr[T] have
-    different dimensions

setup.py

@@ -8,7 +8,7 @@
 
 setup(
     name="pyqn",
-    version="1.3",
+    version="1.3.2",
     description="A package for managing physical units and quantities",
     long_description=long_description,
     long_description_content_type="text/x-rst",
@@ -40,7 +40,7 @@
     ],
     extras_require={"dev": ["black", "pytest-cov", "tox", "ipython"]},
     # package_data will include all the resolved globs into both the wheel and sdist
-    #package_data={},
+    # package_data={},
     # no need for MANIFEST.in, which should be reserved only for build-time files
     project_urls={
         "Bug Reports": "https://github.com/xnx/pyqn/issues",

src/pyqn/atom_unit.py

@@ -23,39 +23,45 @@
 # along with PyQn.  If not, see <http://www.gnu.org/licenses/>
 
 import sys
-from pyparsing import Word, Group, Literal, Suppress, ParseException, oneOf,\
-                      Optional
+from pyparsing import Word, Group, Literal, Suppress, ParseException, oneOf, Optional
 from .si import si_prefixes
 from .base_unit import BaseUnit, base_unit_stems
 from .dimensions import Dimensions
 
 # pyparsing stuff for parsing unit strings:
-caps = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+caps = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 lowers = caps.lower()
-letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_0'
-digits = '123456789'
-exponent = Word(digits + '-')
+letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_0"
+digits = "123456789"
+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))
+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.e-10):
-    return abs(f1-f2) <= tol
-def fneq(f1, f2, tol=1.e-10):
+def feq(f1, f2, tol=1.0e-10):
+    return abs(f1 - f2) <= tol
+
+
+def fneq(f1, f2, tol=1.0e-10):
     return not feq(f1, f2, tol)
 
+
 class UnitsError(Exception):
     """
     An Exception class for errors that might occur whilst manipulating units.
 
     """
+
     def __init__(self, error_str):
         self.error_str = error_str
+
     def __str__(self):
         return self.error_str
 
+
 class AtomUnit(object):
     """
     AtomUnit is a class to represent a single BaseUnit, possibly with an SI
@@ -64,22 +70,21 @@ class AtomUnit(object):
     """
 
     def __init__(self, prefix, base_unit, exponent=1):
-        """ Initialize the AtomUnit object. """
+        """Initialize the AtomUnit object."""
 
         self.base_unit = base_unit
         self.exponent = exponent
-        self.dims = self.base_unit.dims ** self.exponent
+        self.dims = self.base_unit.dims**self.exponent
 
         # get the SI prefix (if present), and its 'factor' (10 raised to its
         # the power it represents
-        self.si_fac = 1.
+        self.si_fac = 1.0
         self.prefix = prefix
         if prefix is not None:
             try:
                 self.si_prefix = si_prefixes[prefix]
             except KeyError:
-                raise UnitsError('Invalid or unsupported SI prefix: %s'
-                                                        % prefix)
+                raise UnitsError("Invalid or unsupported SI prefix: %s" % prefix)
             self.si_fac = self.si_prefix.fac
         # now calculate the factor relating this AtomUnit to its
         # corresponding SI unit:
@@ -97,7 +102,7 @@ def parse(self, s_unit_atom):
             uatom_data = uatom.parseString(s_unit_atom)
         except ParseException:
             raise
-            raise UnitsError('Invalid unit atom syntax: %s' % s_unit_atom)
+            raise UnitsError("Invalid unit atom syntax: %s" % s_unit_atom)
 
         # uatom_data comes back as (([prefix], <stem>), [exponent])
         if len(uatom_data[0]) == 1:
@@ -111,7 +116,7 @@ def parse(self, s_unit_atom):
             # properly (ie to mmHg, not to milli-mHg):
             if stem not in base_unit_stems:
                 prefix = None
-                stem = ''.join(uatom_data[0])
+                stem = "".join(uatom_data[0])
         try:
             base_unit = base_unit_stems[stem]
         except:
@@ -124,18 +129,18 @@ def parse(self, s_unit_atom):
         return AtomUnit(prefix, base_unit, exponent)
 
     def __pow__(self, power):
-        """ Return the current AtomUnit raised to a specified power. """
+        """Return the current AtomUnit raised to a specified power."""
         return AtomUnit(self.prefix, self.base_unit, self.exponent * power)
 
     def __str__(self):
-        """ String representation of this AtomUnit. """
-        s = ''
+        """String representation of this AtomUnit."""
+        s = ""
         if self.prefix:
             s = self.prefix
-        s_exponent = ''
+        s_exponent = ""
         if self.exponent != 1:
             s_exponent = str(self.exponent)
-        return ''.join([s, str(self.base_unit), s_exponent])
+        return "".join([s, str(self.base_unit), s_exponent])
 
     def __repr__(self):
         return str(self)
@@ -150,4 +155,3 @@ def prefix_base_eq(self, other):
         if self.prefix == other.prefix and self.base_unit == other.base_unit:
             return True
         return False
-