Added support for siunitx formatting.

Added support for generating siunitx commands in the __format__
functions for Quantity, Measurment, and Unit classes.

This adds a new code, 'Lx', to the formatting spec, that if present will
trigger the LaTeX siunitx formatting. All other formatting options in
the spec string are be passed through.

Currently does not accept siunit options.

pint/formatting.py

@@ -190,6 +190,43 @@ def format_unit(unit, spec):
     return result
 
 
+def siunitx_format_unit(units):
+  '''Returns LaTeX code for the unit that can be put into an siunitx command.'''
+  # NOTE: unit registry is required to identify unit prefixes.
+  registry = units._REGISTRY
+
+  def _tothe(power):
+    if power == 1:
+      return ''
+    elif power == 2:
+      return r'\squared'
+    elif power == 3:
+      return r'\cubed'
+    else:
+      return r'\tothe{%d}' % (power)
+
+  l = []
+  # loop through all units in the container
+  for unit, power in sorted(units._units.items()):
+    # remove unit prefix if it exists
+    # siunit supports \prefix commands
+    prefix = None
+    for p in registry._prefixes.values():
+      p = str(p)
+      if len(p) > 0 and unit.find(p) == 0:
+        prefix = p
+        unit = unit.replace( prefix, '', 1 )
+        
+    if power < 0:
+      l.append(r'\per')
+    if not prefix is None:
+      l.append(r'\{0}'.format(prefix))
+    l.append(r'\{0}'.format(unit))
+    l.append(r'{0}'.format(_tothe(abs(power))))
+
+  return ''.join(l)
+
+
 def remove_custom_flags(spec):
     for flag in _KNOWN_TYPES:
          if flag:

pint/measurement.py

@@ -10,7 +10,7 @@
 from __future__ import division, unicode_literals, print_function, absolute_import
 
 from .compat import ufloat
-from .formatting import _FORMATS
+from .formatting import _FORMATS, siunitx_format_unit
 
 MISSING = object()
 
@@ -65,6 +65,22 @@ class _Measurement(object):
         return '{0}'.format(self)
 
     def __format__(self, spec):
+        # special cases
+        if 'Lx' in spec: # the LaTeX siunitx code
+          # the uncertainties module supports formatting 
+          # numbers in value(unc) notation (i.e. 1.23(45) instead of 1.23 +/- 0.45),
+          # which siunitx actually accepts as input. we just need to give the 'S'
+          # formatting option for the uncertainties module.
+          spec = spec.replace('Lx','S')
+          # todo: add support for extracting options
+          opts = 'separate-uncertainty=true'
+          mstr = format( self.magnitude, spec )
+          ustr = siunitx_format_unit(self.units)
+          ret = r'\SI[%s]{%s}{%s}'%( opts, mstr, ustr )
+          return ret
+
+
+        # standard cases
         if 'L' in spec:
             newpm = pm = r'  \pm  '
             pars = _FORMATS['L']['parentheses_fmt']

pint/quantity.py

@@ -15,7 +15,7 @@ import operator
 import functools
 import bisect
 
-from .formatting import remove_custom_flags
+from .formatting import remove_custom_flags, siunitx_format_unit
 from .errors import (DimensionalityError, OffsetUnitCalculusError,
                      UndefinedUnitError)
 from .definitions import UnitDefinition
@@ -118,6 +118,18 @@ class _Quantity(SharedRegistryObject):
 
     def __format__(self, spec):
         spec = spec or self.default_format
+
+        # special cases
+        if 'Lx' in spec: # the LaTeX siunitx code
+          spec = spec.replace('Lx','')
+          # todo: add support for extracting options
+          opts = ''
+          mstr = format(self.magnitude,spec)
+          ustr = siunitx_format_unit(self.units)
+          ret = r'\SI[%s]{%s}{%s}'%( opts, mstr, ustr )
+          return ret
+
+        # standard cases
         if '#' in spec:
             spec = spec.replace('#', '')
             obj = self.to_compact()

pint/testsuite/test_measurement.py

@@ -51,11 +51,13 @@ class TestMeasurement(QuantityTestCase):
         self.assertEqual('{0:L}'.format(m), r'\left(4.00 \pm 0.10\right) second^{2}')
         self.assertEqual('{0:H}'.format(m), '(4.00 &plusmn; 0.10) second<sup>2</sup>')
         self.assertEqual('{0:C}'.format(m), '(4.00+/-0.10) second**2')
+        self.assertEqual('{0:Lx}'.format(m), r'\SI[separate-uncertainty=true]{4.00(10)}{\second\squared}')
         self.assertEqual('{0:.1f}'.format(m), '(4.0 +/- 0.1) second ** 2')
         self.assertEqual('{0:.1fP}'.format(m), '(4.0 ± 0.1) second²')
         self.assertEqual('{0:.1fL}'.format(m), r'\left(4.0 \pm 0.1\right) second^{2}')
         self.assertEqual('{0:.1fH}'.format(m), '(4.0 &plusmn; 0.1) second<sup>2</sup>')
         self.assertEqual('{0:.1fC}'.format(m), '(4.0+/-0.1) second**2')
+        self.assertEqual('{0:.1fLx}'.format(m), '\SI[separate-uncertainty=true]{4.0(1)}{\second\squared}')
 
     def test_format_paru(self):
         v, u = self.Q_(0.20, 's ** 2'), self.Q_(0.01, 's ** 2')
@@ -75,6 +77,8 @@ class TestMeasurement(QuantityTestCase):
         self.assertEqual('{0:.3uL}'.format(m), r'\left(0.2000 \pm 0.0100\right) second^{2}')
         self.assertEqual('{0:.3uH}'.format(m), '(0.2000 &plusmn; 0.0100) second<sup>2</sup>')
         self.assertEqual('{0:.3uC}'.format(m), '(0.2000+/-0.0100) second**2')
+        self.assertEqual('{0:.3uLx}'.format(m), '\SI[separate-uncertainty=true]{0.2000(100)}{\second\squared}')
+        self.assertEqual('{0:.1uLx}'.format(m), '\SI[separate-uncertainty=true]{0.20(1)}{\second\squared}')
 
     def test_format_percu(self):
         self.test_format_perce()

pint/testsuite/test_quantity.py

@@ -104,6 +104,7 @@ class TestQuantity(QuantityTestCase):
                              ('{0:P~}', '4.12345678 kg·m²/s'),
                              ('{0:H~}', '4.12345678 kg m<sup>2</sup>/s'),
                              ('{0:C~}', '4.12345678 kg*m**2/s'),
+                             ('{0:Lx}', r'\SI[]{4.12345678}{\kilo\gram\meter\squared\per\second}'),
                              ):
             self.assertEqual(spec.format(x), result)
 

pint/testsuite/test_unit.py

@@ -32,6 +32,7 @@ class TestUnit(QuantityTestCase):
                              ('{0:P}', 'kilogram·meter²/second'),
                              ('{0:H}', 'kilogram meter<sup>2</sup>/second'),
                              ('{0:C}', 'kilogram*meter**2/second'),
+                             ('{0:Lx}', r'\si[]{\kilo\gram\meter\squared\per\second}'),
                              ('{0:~}', 'kg * m ** 2 / s'),
                              ('{0:L~}', r'\frac{kg \cdot m^{2}}{s}'),
                              ('{0:P~}', 'kg·m²/s'),

pint/unit.py

@@ -30,6 +30,7 @@ from .util import (logger, pi_theorem, solve_dependencies, ParserHelper,
                    find_shortest_path, UnitsContainer, _is_dim,
                    SharedRegistryObject, to_units_container)
 from .compat import tokenizer, string_types, NUMERIC_TYPES, long_type, zip_longest
+from .formatting import siunitx_format_unit
 from .definitions import (Definition, UnitDefinition, PrefixDefinition,
                           DimensionDefinition)
 from .converters import ScaleConverter
@@ -99,6 +100,13 @@ class _Unit(SharedRegistryObject):
 
     def __format__(self, spec):
         spec = spec or self.default_format
+        # special cases
+        if 'Lx' in spec: # the LaTeX siunitx code
+          opts = ''
+          ustr = siunitx_format_unit(self)
+          ret = r'\si[%s]{%s}'%( opts, ustr )
+          return ret
+
 
         if '~' in spec:
             units = UnitsContainer(dict((self._REGISTRY._get_symbol(key),

pint/util.py

@@ -22,7 +22,7 @@ from token import STRING, NAME, OP, NUMBER
 from tokenize import untokenize
 
 from .compat import string_types, tokenizer, lru_cache, NullHandler, maketrans, NUMERIC_TYPES
-from .formatting import format_unit
+from .formatting import format_unit,siunitx_format_unit
 from .pint_eval import build_eval_tree
 
 logger = logging.getLogger(__name__)