Source code for pint.measurement

"""
    pint.measurement
    ~~~~~~~~~~~~~~~~

    :copyright: 2016 by Pint Authors, see AUTHORS for more details.
    :license: BSD, see LICENSE for more details.
"""
import re

from .compat import ufloat
from .formatting import _FORMATS, siunitx_format_unit
from .quantity import Quantity

MISSING = object()


class Measurement(Quantity):
    """Implements a class to describe a quantity with uncertainty.

    Parameters
    ----------
    value : pint.Quantity or any numeric type
        The expected value of the measurement
    error : pint.Quantity or any numeric type
        The error or uncertainty of the measurement

    Returns
    -------

    """

    def __new__(cls, value, error, units=MISSING):
        if units is MISSING:
            try:
                value, units = value.magnitude, value.units
            except AttributeError:
                # if called with two arguments and the first looks like a ufloat
                # then assume the second argument is the units, keep value intact
                if hasattr(value, "nominal_value"):
                    units = error
                    error = MISSING  # used for check below
                else:
                    units = ""
        try:
            error = error.to(units).magnitude
        except AttributeError:
            pass

        if error is MISSING:
            mag = value
        elif error < 0:
            raise ValueError(
                "The magnitude of the error cannot be negative".format(value, error)
            )
        else:
            mag = ufloat(value, error)

        inst = super().__new__(cls, mag, units)
        return inst

    @property
    def value(self):
        return self._REGISTRY.Quantity(self.magnitude.nominal_value, self.units)

    @property
    def error(self):
        return self._REGISTRY.Quantity(self.magnitude.std_dev, self.units)

    @property
    def rel(self):
        return float(abs(self.magnitude.std_dev / self.magnitude.nominal_value))

    def __reduce__(self):
        # See notes in Quantity.__reduce__
        from . import _unpickle

        return _unpickle, (Measurement, self.magnitude, self._units)

    def __repr__(self):
        return "<Measurement({}, {}, {})>".format(
            self.magnitude.nominal_value, self.magnitude.std_dev, self.units
        )

    def __str__(self):
        return "{}".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)
            return r"\SI[%s]{%s}{%s}" % (opts, mstr, ustr)

        # standard cases
        if "L" in spec:
            newpm = pm = r"  \pm  "
            pars = _FORMATS["L"]["parentheses_fmt"]
        elif "P" in spec:
            newpm = pm = "±"
            pars = _FORMATS["P"]["parentheses_fmt"]
        else:
            newpm = pm = "+/-"
            pars = _FORMATS[""]["parentheses_fmt"]

        if "C" in spec:
            sp = ""
            newspec = spec.replace("C", "")
            pars = _FORMATS["C"]["parentheses_fmt"]
        else:
            sp = " "
            newspec = spec

        if "H" in spec:
            newpm = "&plusmn;"
            newspec = spec.replace("H", "")
            pars = _FORMATS["H"]["parentheses_fmt"]

        mag = format(self.magnitude, newspec).replace(pm, sp + newpm + sp)
        if "(" in mag:
            # Exponential format has its own parentheses
            pars = "{}"

        if "L" in newspec and "S" in newspec:
            mag = mag.replace("(", r"\left(").replace(")", r"\right)")

        if "L" in newspec or "H" in spec:
            space = r"\ "
        else:
            space = " "

        ustr = format(self.units, spec)
        if not ("uS" in newspec or "ue" in newspec or "u%" in newspec):
            mag = pars.format(mag)

        if "H" in spec:
            # Fix exponential format
            mag = re.sub(r"\)e\+0?(\d+)", r")×10^{\1}", mag)
            mag = re.sub(r"\)e-0?(\d+)", r")×10^{-\1}", mag)

            assert ustr[:2] == r"\["
            assert ustr[-2:] == r"\]"
            return r"\[" + mag + space + ustr[2:]
        else:
            return mag + space + ustr


_Measurement = Measurement


def build_measurement_class(registry):

    if ufloat is None:

        class Measurement:
            _REGISTRY = registry

            def __init__(self, *args):
                raise RuntimeError(
                    "Pint requires the 'uncertainties' package to create a Measurement object."
                )

    else:

        class Measurement(_Measurement):
            _REGISTRY = registry

    return Measurement