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# Copyright (c) 2008-2016 MetPy Developers. |
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# Distributed under the terms of the BSD 3-Clause License. |
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# SPDX-License-Identifier: BSD-3-Clause |
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r"""Module to provide unit support. |
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This makes use of the :mod:`pint` library and sets up the default settings |
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for good temperature support. |
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Attributes |
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---------- |
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units : :class:`pint.UnitRegistry` |
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The unit registry used throughout the package. Any use of units in MetPy should |
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import this registry and use it to grab units. |
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""" |
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from __future__ import division |
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import functools |
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import numpy as np |
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import pint |
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import pint.unit |
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UndefinedUnitError = pint.UndefinedUnitError |
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DimensionalityError = pint.DimensionalityError |
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units = pint.UnitRegistry(autoconvert_offset_to_baseunit=True) |
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# For pint 0.6, this is the best way to define a dimensionless unit. See pint #185 |
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units.define(pint.unit.UnitDefinition('percent', '%', (), |
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pint.converters.ScaleConverter(0.01))) |
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def concatenate(arrs, axis=0): |
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r"""Concatenate multiple values into a new unitized object. |
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This is essentially a unit-aware version of `numpy.concatenate`. All items |
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must be able to be converted to the same units. If an item has no units, it will be given |
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those of the rest of the collection, without conversion. The first units found in the |
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arguments is used as the final output units. |
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Parameters |
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---------- |
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arrs : Sequence of arrays |
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The items to be joined together |
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axis : integer, optional |
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The array axis along which to join the arrays. Defaults to 0 (the first dimension) |
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Returns |
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------- |
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`pint.Quantity` |
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New container with the value passed in and units corresponding to the first item. |
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""" |
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dest = 'dimensionless' |
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for a in arrs: |
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if hasattr(a, 'units'): |
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dest = a.units |
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break |
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data = [] |
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for a in arrs: |
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if hasattr(a, 'to'): |
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a = a.to(dest).magnitude |
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data.append(np.atleast_1d(a)) |
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return units.Quantity(np.concatenate(data, axis=axis), dest) |
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def atleast_1d(*arrs): |
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r"""Convert inputs to arrays with at least one dimension. |
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Scalars are converted to 1-dimensional arrays, whilst other |
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higher-dimensional inputs are preserved. This is a thin wrapper |
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around `numpy.atleast_1d` to preserve units. |
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Parameters |
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---------- |
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arrs : arbitrary positional arguments |
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Input arrays to be converted if necessary |
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Returns |
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------- |
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`pint.Quantity` |
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A single quantity or a list of quantities, matching the number of inputs. |
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""" |
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mags = [a.magnitude for a in arrs] |
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orig_units = [a.units for a in arrs] |
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ret = np.atleast_1d(*mags) |
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if len(mags) == 1: |
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return units.Quantity(ret, orig_units[0]) |
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return [units.Quantity(m, u) for m, u in zip(ret, orig_units)] |
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def atleast_2d(*arrs): |
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r"""Convert inputs to arrays with at least two dimensions. |
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Scalars and 1-dimensional arrays are converted to 2-dimensional arrays, |
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whilst other higher-dimensional inputs are preserved. This is a thin wrapper |
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around `numpy.atleast_2d` to preserve units. |
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Parameters |
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---------- |
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arrs : arbitrary positional arguments |
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Input arrays to be converted if necessary |
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Returns |
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------- |
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`pint.Quantity` |
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A single quantity or a list of quantities, matching the number of inputs. |
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""" |
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mags = [a.magnitude for a in arrs] |
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orig_units = [a.units for a in arrs] |
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ret = np.atleast_2d(*mags) |
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if len(mags) == 1: |
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return units.Quantity(ret, orig_units[0]) |
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return [units.Quantity(m, u) for m, u in zip(ret, orig_units)] |
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def masked_array(data, data_units=None, **kwargs): |
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"""Create a :class:`numpy.ma.MaskedArray` with units attached. |
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This is a thin wrapper around :func:`numpy.ma.masked_array` that ensures that |
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units are properly attached to the result (otherwise units are silently lost). Units |
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are taken from the ``units`` argument, or if this is ``None``, the units on ``data`` |
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are used. |
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Parameters |
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---------- |
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data : array_like |
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The source data. If ``units`` is `None`, this should be a `pint.Quantity` with |
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the desired units. |
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data_units : str or `pint.Unit` |
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The units for the resulting `pint.Quantity` |
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**kwargs : Arbitrary keyword arguments passed to `numpy.ma.masked_array` |
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Returns |
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------- |
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`pint.Quantity` |
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""" |
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if data_units is None: |
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data_units = data.units |
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return units.Quantity(np.ma.masked_array(data, **kwargs), data_units) |
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def _check_argument_units(args, dimensionality): |
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"""Yield arguments with improper dimensionality.""" |
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for arg, val in args.items(): |
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# Get the needed dimensionality (for printing) as well as cached, parsed version |
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# for this argument. |
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try: |
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need, parsed = dimensionality[arg] |
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except KeyError: |
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# Argument did not have units specified in decorator |
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continue |
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# See if the value passed in is appropriate |
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try: |
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if val.dimensionality != parsed: |
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yield arg, val.units, need |
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# No dimensionality |
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except AttributeError: |
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# If this argument is dimensionless, don't worry |
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if parsed != '': |
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yield arg, 'none', need |
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def check_units(*units_by_pos, **units_by_name): |
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"""Create a decorator to check units of function arguments.""" |
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try: |
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from inspect import signature |
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def dec(func): |
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# Match the signature of the function to the arguments given to the decorator |
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sig = signature(func) |
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bound_units = sig.bind_partial(*units_by_pos, **units_by_name) |
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# Convert our specified dimensionality (e.g. "[pressure]") to one used by |
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# pint directly (e.g. "[mass] / [length] / [time]**2). This is for both efficiency |
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# reasons and to ensure that problems with the decorator are caught at import, |
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# rather than runtime. |
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dims = {name: (orig, units.get_dimensionality(orig.replace('dimensionless', ''))) |
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for name, orig in bound_units.arguments.items()} |
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@functools.wraps(func) |
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def wrapper(*args, **kwargs): |
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# Match all passed in value to their proper arguments so we can check units |
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bound_args = sig.bind(*args, **kwargs) |
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bad = list(_check_argument_units(bound_args.arguments, dims)) |
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# If there are any bad units, emit a proper error message making it clear |
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# what went wrong. |
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if bad: |
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msg = '`{0}` given arguments with incorrect units: {1}.'.format( |
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func.__name__, |
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', '.join('`{}` requires "{}" but given "{}"'.format(arg, req, given) |
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for arg, given, req in bad)) |
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if 'none' in msg: |
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msg += ('\nAny variable `x` can be assigned a unit as follows:\n' |
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' from metpy.units import units\n' |
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' x = x * units.meter / units.second') |
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raise ValueError(msg) |
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return func(*args, **kwargs) |
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return wrapper |
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# signature() only available on Python >= 3.3, so for 2.7 we just do nothing. |
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except ImportError: |
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def dec(func): |
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return func |
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return dec |
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try: |
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# Try to enable pint's built-in support |
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units.setup_matplotlib() |
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except (AttributeError, RuntimeError): # Pint's not available, try to enable our own |
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import matplotlib.units as munits |
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# Inheriting from object fixes the fact that matplotlib 1.4 doesn't |
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# TODO: Remove object when we drop support for matplotlib 1.4 |
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class PintAxisInfo(munits.AxisInfo, object): |
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"""Support default axis and tick labeling and default limits.""" |
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def __init__(self, units): |
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"""Set the default label to the pretty-print of the unit.""" |
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super(PintAxisInfo, self).__init__(label='{:P}'.format(units)) |
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# TODO: Remove object when we drop support for matplotlib 1.4 |
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class PintConverter(munits.ConversionInterface, object): |
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"""Implement support for pint within matplotlib's unit conversion framework.""" |
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def __init__(self, registry): |
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"""Initialize converter for pint units.""" |
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super(PintConverter, self).__init__() |
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self._reg = registry |
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def convert(self, value, unit, axis): |
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"""Convert :`Quantity` instances for matplotlib to use.""" |
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if isinstance(value, (tuple, list)): |
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return [self._convert_value(v, unit, axis) for v in value] |
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else: |
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return self._convert_value(value, unit, axis) |
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def _convert_value(self, value, unit, axis): |
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"""Handle converting using attached unit or falling back to axis units.""" |
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if hasattr(value, 'units'): |
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return value.to(unit).magnitude |
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else: |
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return self._reg.Quantity(value, axis.get_units()).to(unit).magnitude |
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@staticmethod |
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def axisinfo(unit, axis): |
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"""Return axis information for this particular unit.""" |
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return PintAxisInfo(unit) |
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@staticmethod |
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def default_units(x, axis): |
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"""Get the default unit to use for the given combination of unit and axis.""" |
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return getattr(x, 'units', None) |
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# Register the class |
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munits.registry[units.Quantity] = PintConverter(units) |
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del munits |
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del pint |
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