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# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
Utilities shared by the different formats.
"""
from __future__ import (absolute_import, division, print_function,
unicode_literals)
import warnings
from fractions import Fraction
from ...extern import six
from ...extern.six.moves import zip
from ...utils.misc import did_you_mean
def get_grouped_by_powers(bases, powers):
"""
Groups the powers and bases in the given
`~astropy.units.CompositeUnit` into positive powers and
negative powers for easy display on either side of a solidus.
Parameters
----------
bases : list of `astropy.units.UnitBase` instances
powers : list of ints
Returns
-------
positives, negatives : tuple of lists
Each element in each list is tuple of the form (*base*,
*power*). The negatives have the sign of their power reversed
(i.e. the powers are all positive).
"""
positive = []
negative = []
for base, power in zip(bases, powers):
if power < 0:
negative.append((base, -power))
elif power > 0:
positive.append((base, power))
else:
raise ValueError("Unit with 0 power")
return positive, negative
def split_mantissa_exponent(v):
"""
Given a number, split it into its mantissa and base 10 exponent
parts, each as strings. If the exponent is too small, it may be
returned as the empty string.
The precise rules are based on Python's "general purpose" (`g`)
formatting.
Parameters
----------
v : float
Returns
-------
mantissa, exponent : tuple of strings
"""
x = "{0:.8g}".format(v).split('e')
if x[0] != '1.' + '0' * (len(x[0]) - 2):
m = x[0]
else:
m = ''
if len(x) == 2:
ex = x[1].lstrip("0+")
if len(ex) > 0 and ex[0] == '-':
ex = '-' + ex[1:].lstrip('0')
else:
ex = ''
return m, ex
def decompose_to_known_units(unit, func):
"""
Partially decomposes a unit so it is only composed of units that
are "known" to a given format.
Parameters
----------
unit : `~astropy.units.UnitBase` instance
func : callable
This function will be called to determine if a given unit is
"known". If the unit is not known, this function should raise a
`ValueError`.
Returns
-------
unit : `~astropy.units.UnitBase` instance
A flattened unit.
"""
from .. import core
if isinstance(unit, core.CompositeUnit):
new_unit = core.Unit(unit.scale)
for base, power in zip(unit.bases, unit.powers):
new_unit = new_unit * decompose_to_known_units(base, func) ** power
return new_unit
elif isinstance(unit, core.NamedUnit):
try:
func(unit)
except ValueError:
if isinstance(unit, core.Unit):
return decompose_to_known_units(unit._represents, func)
raise
return unit
def format_power(power):
"""
Converts a value for a power (which may be floating point or a
`fractions.Fraction` object), into a string either looking like
an integer or a fraction.
"""
if not isinstance(power, Fraction):
if power % 1.0 != 0.0:
frac = Fraction.from_float(power)
power = frac.limit_denominator(10)
if power.denominator == 1:
power = int(power.numerator)
else:
power = int(power)
return six.text_type(power)
def _try_decomposed(unit, format_decomposed):
represents = getattr(unit, '_represents', None)
if represents is not None:
try:
represents_string = format_decomposed(represents)
except ValueError:
pass
else:
return represents_string
decomposed = unit.decompose()
if decomposed is not unit:
try:
decompose_string = format_decomposed(decomposed)
except ValueError:
pass
else:
return decompose_string
return None
def did_you_mean_units(s, all_units, deprecated_units, format_decomposed):
"""
A wrapper around `astropy.utils.misc.did_you_mean` that deals with
the display of deprecated units.
Parameters
----------
s : str
The invalid unit string
all_units : dict
A mapping from valid unit names to unit objects.
deprecated_units : sequence
The deprecated unit names
format_decomposed : callable
A function to turn a decomposed version of the unit into a
string. Should return `None` if not possible
Returns
-------
msg : str
A string message with a list of alternatives, or the empty
string.
"""
def fix_deprecated(x):
if x in deprecated_units:
results = [x + ' (deprecated)']
decomposed = _try_decomposed(
all_units[x], format_decomposed)
if decomposed is not None:
results.append(decomposed)
return results
return (x,)
return did_you_mean(s, all_units, fix=fix_deprecated)
def unit_deprecation_warning(s, unit, standard_name, format_decomposed):
"""
Raises a UnitsWarning about a deprecated unit in a given format.
Suggests a decomposed alternative if one is available.
Parameters
----------
s : str
The deprecated unit name.
unit : astropy.units.core.UnitBase
The unit object.
standard_name : str
The name of the format for which the unit is deprecated.
format_decomposed : callable
A function to turn a decomposed version of the unit into a
string. Should return `None` if not possible
"""
from ..core import UnitsWarning
message = "The unit '{0}' has been deprecated in the {1} standard.".format(
s, standard_name)
decomposed = _try_decomposed(unit, format_decomposed)
if decomposed is not None:
message += " Suggested: {0}.".format(decomposed)
warnings.warn(message, UnitsWarning)
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