Adding pint-convert script (see #1012)

2 files changed, 116 insertions, 1 deletions

diff --git a/pint/constants_en.txt b/pint/constants_en.txt
index fa485fa..c3ecbf1 100644
--- a/pint/constants_en.txt
+++ b/pint/constants_en.txt
@@ -8,7 +8,7 @@
 #### MATHEMATICAL CONSTANTS ####
 # As computed by Maxima with fpprec:50
 
-pi    = 3.1415926535897932384626433832795028841971693993751 = π  # pi
+pi     = 3.1415926535897932384626433832795028841971693993751 = π  # pi
 tansec = 4.8481368111333441675396429478852851658848753880815e-6   # tangent of 1 arc-second ~ arc_second/radian
 ln10   = 2.3025850929940456840179914546843642076011014886288      # natural logarithm of 10
 wien_x = 4.9651142317442763036987591313228939440555849867973      # solution to (x-5)*exp(x)+5 = 0 => x = W(5/exp(5))+5
diff --git a/pint/pint-convert b/pint/pint-convert
new file mode 100755
index 0000000..d2540a3
--- /dev/null
+++ b/pint/pint-convert
@@ -0,0 +1,115 @@
+#!/usr/bin/env python3
+
+"""
+    pint_convert
+    ~~~~~~~~~~~~
+
+    :copyright: 2020 by Pint Authors, see AUTHORS for more details.
+    :license: BSD, see LICENSE for more details.
+"""
+
+import argparse
+from pint import UnitRegistry
+import sys
+import re
+
+parser = argparse.ArgumentParser(description='Unit converter.')
+parser.add_argument('-s', '--system', metavar='sys', default='SI', help='unit system to convert to (default: SI)')
+parser.add_argument('-p', '--prec', metavar='n', type=int, default=12, help='number of maximum significant figures (default: 12)')
+parser.add_argument('-u', '--prec-unc', metavar='n', type=int, default=2, help='number of maximum uncertainty digits (default: 2)')
+parser.add_argument('-U', '--no-unc', dest='unc', action='store_false', help='ignore uncertainties in constants')
+parser.add_argument('-C', '--no-corr', dest='corr', action='store_false', help='ignore correlations between constants')
+parser.add_argument('fr', metavar='from', type=str, help='unit or quantity to convert from')
+parser.add_argument('to', type=str, nargs='?', help='unit to convert to')
+args = parser.parse_args()
+
+ureg = UnitRegistry()
+ureg.auto_reduce_dimensions = True
+ureg.autoconvert_offset_to_baseunit = True
+ureg.enable_contexts('Gau', 'ESU', 'sp', 'energy', 'boltzmann')
+ureg.default_system = args.system
+
+if args.unc:
+    import uncertainties
+    # Measured constans subject to correlation
+    #  R_i: Rydberg constant
+    #  g_e: Electron g factor
+    #  m_u: Atomic mass constant
+    #  m_e: Electron mass
+    #  m_p: Proton mass
+    #  m_n: Neutron mass
+    R_i = (ureg._units['R_inf'].converter.scale, 0.0000000000021e7)
+    g_e = (ureg._units['g_e'].converter.scale,   0.00000000000035)
+    m_u = (ureg._units['m_u'].converter.scale,   0.00000000050e-27)
+    m_e = (ureg._units['m_e'].converter.scale,   0.00000000028e-30)
+    m_p = (ureg._units['m_p'].converter.scale,   0.00000000051e-27)
+    m_n = (ureg._units['m_n'].converter.scale,   0.00000000095e-27)
+    if args.corr:
+        # Correlation matrix between measured constants (to be completed below)
+        #          R_i       g_e       m_u       m_e       m_p       m_n
+        corr = [[  1.0    , -0.00206,  0.00369,  0.00436,  0.00194,  0.00233],  # R_i
+                [ -0.00206,  1.0    ,  0.99029,  0.99490,  0.97560,  0.52445],  # g_e
+                [  0.00369,  0.99029,  1.0    ,  0.99536,  0.98516,  0.52959],  # m_u
+                [  0.00436,  0.99490,  0.99536,  1.0    ,  0.98058,  0.52714],  # m_e
+                [  0.00194,  0.97560,  0.98516,  0.98058,  1.0    ,  0.51521],  # m_p
+                [  0.00233,  0.52445,  0.52959,  0.52714,  0.51521,  1.0    ]]  # m_n
+        (R_i, g_e, m_u, m_e, m_p, m_n) = uncertainties.correlated_values_norm([R_i, g_e, m_u, m_e, m_p, m_n], corr)
+    else:
+        R_i = uncertainties.ufloat(*R_i)
+        g_e = uncertainties.ufloat(*g_e)
+        m_u = uncertainties.ufloat(*m_u)
+        m_e = uncertainties.ufloat(*m_e)
+        m_p = uncertainties.ufloat(*m_p)
+        m_n = uncertainties.ufloat(*m_n)
+    ureg._units['R_inf'].converter.scale = R_i
+    ureg._units['g_e'].converter.scale   = g_e
+    ureg._units['m_u'].converter.scale   = m_u
+    ureg._units['m_e'].converter.scale   = m_e
+    ureg._units['m_p'].converter.scale   = m_p
+    ureg._units['m_n'].converter.scale   = m_n
+
+    # Measured constants with zero correlation
+    ureg._units['gravitational_constant'].converter.scale = uncertainties.ufloat(ureg._units['gravitational_constant'].converter.scale, 0.00015e-11)
+    ureg._units['d_220'].converter.scale                  = uncertainties.ufloat(ureg._units['d_220'].converter.scale,                  0.000000032e-10)
+    ureg._units['K_alpha_Cu_d_220'].converter.scale       = uncertainties.ufloat(ureg._units['K_alpha_Cu_d_220'].converter.scale,       0.00000022)
+    ureg._units['K_alpha_Mo_d_220'].converter.scale       = uncertainties.ufloat(ureg._units['K_alpha_Mo_d_220'].converter.scale,       0.00000019)
+    ureg._units['K_alpha_W_d_220'].converter.scale        = uncertainties.ufloat(ureg._units['K_alpha_W_d_220'].converter.scale,        0.000000098)
+
+    ureg._root_units_cache = dict()
+    ureg._build_cache()
+
+def convert(u_from, u_to=None, unc=None, factor=None):
+    q = ureg.Quantity(u_from)
+    fmt = '.{}g'.format(args.prec)
+    if unc:
+        q = q.plus_minus(unc)
+    if u_to:
+        nq = q.to(u_to)
+    else:
+        nq = q.to_base_units()
+    if (factor):
+        q *= ureg.Quantity(factor)
+        nq *= ureg.Quantity(factor).to_base_units()
+    prec_unc = use_unc(nq.magnitude, fmt, args.prec_unc)
+    if (prec_unc > 0):
+        fmt = '.{}uS'.format(prec_unc)
+    else:
+        try:
+            nq = nq.magnitude.n * nq.units
+        except:
+            pass
+    fmt = '{:' + fmt + '} {:~P}'
+    print(('{:} = ' + fmt).format(q, nq.magnitude, nq.units))
+
+def use_unc(num, fmt, prec_unc):
+    unc = 0
+    try:
+        if (isinstance(num, uncertainties.UFloat)):
+            full = ('{:'+fmt+'}').format(num)
+            unc = re.search(r'\+\/-[0.]*([\d.]*)', full).group(1)
+            unc = len(unc.replace('.', ''))
+    except:
+        pass
+    return max(0, min(prec_unc, unc))
+
+convert(args.fr, args.to)