Source code for astropy.units.function.core

# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Function Units and Quantities."""

from abc import ABCMeta, abstractmethod

import numpy as np

from .. import (Unit, UnitBase, UnitsError, UnitTypeError,
                dimensionless_unscaled, Quantity)

__all__ = ['FunctionUnitBase', 'FunctionQuantity']

SUPPORTED_UFUNCS = set(getattr(np.core.umath, ufunc) for ufunc in (
    'isfinite', 'isinf', 'isnan', 'sign', 'signbit',
    'rint', 'floor', 'ceil', 'trunc', 'power',
    '_ones_like', 'ones_like', 'positive') if hasattr(np.core.umath, ufunc))

# TODO: the following could work if helper changed relative to Quantity:
# - spacing should return dimensionless, not same unit
# - negative should negate unit too,
# - add, subtract, comparisons can work if units added/subtracted

SUPPORTED_FUNCTIONS = set(getattr(np, function) for function in
                          ('clip', 'trace', 'mean', 'min', 'max', 'round'))


# subclassing UnitBase or CompositeUnit was found to be problematic, requiring
# a large number of overrides. Hence, define new class.
[docs]class FunctionUnitBase(metaclass=ABCMeta): """Abstract base class for function units. Function units are functions containing a physical unit, such as dB(mW). Most of the arithmetic operations on function units are defined in this base class. While instantiation is defined, this class should not be used directly. Rather, subclasses should be used that override the abstract properties `_default_function_unit` and `_quantity_class`, and the abstract methods `from_physical`, and `to_physical`. Parameters ---------- physical_unit : `~astropy.units.Unit` or `string` Unit that is encapsulated within the function unit. If not given, dimensionless. function_unit : `~astropy.units.Unit` or `string` By default, the same as the function unit set by the subclass. """ # ↓↓↓ the following four need to be set by subclasses # Make this a property so we can ensure subclasses define it. @property @abstractmethod def _default_function_unit(self): """Default function unit corresponding to the function. This property should be overridden by subclasses, with, e.g., `~astropy.unit.MagUnit` returning `~astropy.unit.mag`. """ # This has to be a property because the function quantity will not be # known at unit definition time, as it gets defined after. @property @abstractmethod def _quantity_class(self): """Function quantity class corresponding to this function unit. This property should be overridden by subclasses, with, e.g., `~astropy.unit.MagUnit` returning `~astropy.unit.Magnitude`. """
[docs] @abstractmethod def from_physical(self, x): """Transformation from value in physical to value in function units. This method should be overridden by subclasses. It is used to provide automatic transformations using an equivalency. """
[docs] @abstractmethod def to_physical(self, x): """Transformation from value in function to value in physical units. This method should be overridden by subclasses. It is used to provide automatic transformations using an equivalency. """
# ↑↑↑ the above four need to be set by subclasses # have priority over arrays, regular units, and regular quantities __array_priority__ = 30000 def __init__(self, physical_unit=None, function_unit=None): if physical_unit is None: self._physical_unit = dimensionless_unscaled else: self._physical_unit = Unit(physical_unit) if (not isinstance(self._physical_unit, UnitBase) or self._physical_unit.is_equivalent( self._default_function_unit)): raise ValueError("Unit {0} is not a physical unit." .format(self._physical_unit)) if function_unit is None: self._function_unit = self._default_function_unit else: # any function unit should be equivalent to subclass default function_unit = Unit(getattr(function_unit, 'function_unit', function_unit)) if function_unit.is_equivalent(self._default_function_unit): self._function_unit = function_unit else: raise ValueError("Cannot initialize '{0}' instance with " "function unit '{1}', as it is not " "equivalent to default function unit '{2}'." .format(self.__class__.__name__, function_unit, self._default_function_unit)) def _copy(self, physical_unit=None): """Copy oneself, possibly with a different physical unit.""" if physical_unit is None: physical_unit = self.physical_unit return self.__class__(physical_unit, self.function_unit) @property def physical_unit(self): return self._physical_unit @property def function_unit(self): return self._function_unit @property def equivalencies(self): """List of equivalencies between function and physical units. Uses the `from_physical` and `to_physical` methods. """ return [(self, self.physical_unit, self.to_physical, self.from_physical)] # ↓↓↓ properties/methods required to behave like a unit
[docs] def decompose(self, bases=set()): """Copy the current unit with the physical unit decomposed. For details, see `~astropy.units.UnitBase.decompose`. """ return self._copy(self.physical_unit.decompose(bases))
@property def si(self): """Copy the current function unit with the physical unit in SI.""" return self._copy(self.physical_unit.si) @property def cgs(self): """Copy the current function unit with the physical unit in CGS.""" return self._copy(self.physical_unit.cgs) def _get_physical_type_id(self): """Get physical type corresponding to physical unit.""" return self.physical_unit._get_physical_type_id() @property def physical_type(self): """Return the physical type of the physical unit (e.g., 'length').""" return self.physical_unit.physical_type
[docs] def is_equivalent(self, other, equivalencies=[]): """ Returns `True` if this unit is equivalent to ``other``. Parameters ---------- other : unit object or string or tuple The unit to convert to. If a tuple of units is specified, this method returns true if the unit matches any of those in the tuple. equivalencies : list of equivalence pairs, optional A list of equivalence pairs to try if the units are not directly convertible. See :ref:`unit_equivalencies`. This list is in addition to the built-in equivalencies between the function unit and the physical one, as well as possible global defaults set by, e.g., `~astropy.units.set_enabled_equivalencies`. Use `None` to turn off any global equivalencies. Returns ------- bool """ if isinstance(other, tuple): return any(self.is_equivalent(u, equivalencies=equivalencies) for u in other) other_physical_unit = getattr(other, 'physical_unit', ( dimensionless_unscaled if self.function_unit.is_equivalent(other) else other)) return self.physical_unit.is_equivalent(other_physical_unit, equivalencies)
[docs] def to(self, other, value=1., equivalencies=[]): """ Return the converted values in the specified unit. Parameters ---------- other : `~astropy.units.Unit` object, `~astropy.units.function.FunctionUnitBase` object or string The unit to convert to. value : scalar int or float, or sequence convertible to array, optional Value(s) in the current unit to be converted to the specified unit. If not provided, defaults to 1.0. equivalencies : list of equivalence pairs, optional A list of equivalence pairs to try if the units are not directly convertible. See :ref:`unit_equivalencies`. This list is in meant to treat only equivalencies between different physical units; the build-in equivalency between the function unit and the physical one is automatically taken into account. Returns ------- values : scalar or array Converted value(s). Input value sequences are returned as numpy arrays. Raises ------ UnitsError If units are inconsistent. """ # conversion to one's own physical unit should be fastest if other is self.physical_unit: return self.to_physical(value) other_function_unit = getattr(other, 'function_unit', other) if self.function_unit.is_equivalent(other_function_unit): # when other is an equivalent function unit: # first convert physical units to other's physical units other_physical_unit = getattr(other, 'physical_unit', dimensionless_unscaled) if self.physical_unit != other_physical_unit: value_other_physical = self.physical_unit.to( other_physical_unit, self.to_physical(value), equivalencies) # make function unit again, in own system value = self.from_physical(value_other_physical) # convert possible difference in function unit (e.g., dex->dB) return self.function_unit.to(other_function_unit, value) else: # when other is not a function unit return self.physical_unit.to(other, self.to_physical(value), equivalencies)
[docs] def is_unity(self): return False
def __eq__(self, other): return (self.physical_unit == getattr(other, 'physical_unit', dimensionless_unscaled) and self.function_unit == getattr(other, 'function_unit', other)) def __ne__(self, other): return not self.__eq__(other) def __mul__(self, other): if isinstance(other, (str, UnitBase, FunctionUnitBase)): if self.physical_unit == dimensionless_unscaled: # If dimensionless, drop back to normal unit and retry. return self.function_unit * other else: raise UnitsError("Cannot multiply a function unit " "with a physical dimension with any unit.") else: # Anything not like a unit, try initialising as a function quantity. try: return self._quantity_class(other, unit=self) except Exception: return NotImplemented def __rmul__(self, other): return self.__mul__(other) def __div__(self, other): if isinstance(other, (str, UnitBase, FunctionUnitBase)): if self.physical_unit == dimensionless_unscaled: # If dimensionless, drop back to normal unit and retry. return self.function_unit / other else: raise UnitsError("Cannot divide a function unit " "with a physical dimension by any unit.") else: # Anything not like a unit, try initialising as a function quantity. try: return self._quantity_class(1./other, unit=self) except Exception: return NotImplemented def __rdiv__(self, other): if isinstance(other, (str, UnitBase, FunctionUnitBase)): if self.physical_unit == dimensionless_unscaled: # If dimensionless, drop back to normal unit and retry. return other / self.function_unit else: raise UnitsError("Cannot divide a function unit " "with a physical dimension into any unit") else: # Don't know what to do with anything not like a unit. return NotImplemented __truediv__ = __div__ __rtruediv__ = __rdiv__ def __pow__(self, power): if power == 0: return dimensionless_unscaled elif power == 1: return self._copy() if self.physical_unit == dimensionless_unscaled: return self.function_unit ** power raise UnitsError("Cannot raise a function unit " "with a physical dimension to any power but 0 or 1.") def __pos__(self): return self._copy()
[docs] def to_string(self, format='generic'): """ Output the unit in the given format as a string. The physical unit is appended, within parentheses, to the function unit, as in "dB(mW)", with both units set using the given format Parameters ---------- format : `astropy.units.format.Base` instance or str The name of a format or a formatter object. If not provided, defaults to the generic format. """ if format not in ('generic', 'unscaled', 'latex'): raise ValueError("Function units cannot be written in {0} format. " "Only 'generic', 'unscaled' and 'latex' are " "supported.".format(format)) self_str = self.function_unit.to_string(format) pu_str = self.physical_unit.to_string(format) if pu_str == '': pu_str = '1' if format == 'latex': self_str += r'$\mathrm{{\left( {0} \right)}}$'.format( pu_str[1:-1]) # need to strip leading and trailing "$" else: self_str += '({0})'.format(pu_str) return self_str
def __str__(self): """Return string representation for unit.""" self_str = str(self.function_unit) pu_str = str(self.physical_unit) if pu_str: self_str += '({0})'.format(pu_str) return self_str def __repr__(self): # By default, try to give a representation using `Unit(<string>)`, # with string such that parsing it would give the correct FunctionUnit. if callable(self.function_unit): return 'Unit("{0}")'.format(self.to_string()) else: return '{0}("{1}"{2})'.format( self.__class__.__name__, self.physical_unit, "" if self.function_unit is self._default_function_unit else ', unit="{0}"'.format(self.function_unit)) def _repr_latex_(self): """ Generate latex representation of unit name. This is used by the IPython notebook to print a unit with a nice layout. Returns ------- Latex string """ return self.to_string('latex') def __hash__(self): return hash((self.function_unit, self.physical_unit))
[docs]class FunctionQuantity(Quantity): """A representation of a (scaled) function of a number with a unit. Function quantities are quantities whose units are functions containing a physical unit, such as dB(mW). Most of the arithmetic operations on function quantities are defined in this base class. While instantiation is also defined here, this class should not be instantiated directly. Rather, subclasses should be made which have ``_unit_class`` pointing back to the corresponding function unit class. Parameters ---------- value : number, sequence of convertible items, `~astropy.units.Quantity`, or `~astropy.units.function.FunctionQuantity` The numerical value of the function quantity. If a number or a `~astropy.units.Quantity` with a function unit, it will be converted to ``unit`` and the physical unit will be inferred from ``unit``. If a `~astropy.units.Quantity` with just a physical unit, it will converted to the function unit, after, if necessary, converting it to the physical unit inferred from ``unit``. unit : string, `~astropy.units.UnitBase` or `~astropy.units.function.FunctionUnitBase` instance, optional For an `~astropy.units.function.FunctionUnitBase` instance, the physical unit will be taken from it; for other input, it will be inferred from ``value``. By default, ``unit`` is set by the subclass. dtype : `~numpy.dtype`, optional The dtype of the resulting Numpy array or scalar that will hold the value. If not provided, it is determined from the input, except that any input that cannot represent float (integer and bool) is converted to float. copy : bool, optional If `True` (default), then the value is copied. Otherwise, a copy will only be made if ``__array__`` returns a copy, if value is a nested sequence, or if a copy is needed to satisfy an explicitly given ``dtype``. (The `False` option is intended mostly for internal use, to speed up initialization where a copy is known to have been made. Use with care.) order : {'C', 'F', 'A'}, optional Specify the order of the array. As in `~numpy.array`. Ignored if the input does not need to be converted and ``copy=False``. subok : bool, optional If `False` (default), the returned array will be forced to be of the class used. Otherwise, subclasses will be passed through. ndmin : int, optional Specifies the minimum number of dimensions that the resulting array should have. Ones will be pre-pended to the shape as needed to meet this requirement. This parameter is ignored if the input is a `~astropy.units.Quantity` and ``copy=False``. Raises ------ TypeError If the value provided is not a Python numeric type. TypeError If the unit provided is not a `~astropy.units.function.FunctionUnitBase` or `~astropy.units.Unit` object, or a parseable string unit. """ _unit_class = None """Default `~astropy.units.function.FunctionUnitBase` subclass. This should be overridden by subclasses. """ # Ensure priority over ndarray, regular Unit & Quantity, and FunctionUnit. __array_priority__ = 40000 # Define functions that work on FunctionQuantity. _supported_ufuncs = SUPPORTED_UFUNCS _supported_functions = SUPPORTED_FUNCTIONS def __new__(cls, value, unit=None, dtype=None, copy=True, order=None, subok=False, ndmin=0): if unit is not None: # Convert possible string input to a (function) unit. unit = Unit(unit) if not isinstance(unit, FunctionUnitBase): # By default, use value's physical unit. value_unit = getattr(value, 'unit', None) if value_unit is None: # if iterable, see if first item has a unit # (mixed lists fail in super call below). try: value_unit = getattr(value[0], 'unit') except Exception: pass physical_unit = getattr(value_unit, 'physical_unit', value_unit) unit = cls._unit_class(physical_unit, function_unit=unit) # initialise! return super().__new__(cls, value, unit, dtype=dtype, copy=copy, order=order, subok=subok, ndmin=ndmin) # ↓↓↓ properties not found in Quantity @property def physical(self): """The physical quantity corresponding the function one.""" return self.to(self.unit.physical_unit) @property def _function_view(self): """View as Quantity with function unit, dropping the physical unit. Use `~astropy.units.quantity.Quantity.value` for just the value. """ return self._new_view(unit=self.unit.function_unit) # ↓↓↓ methods overridden to change the behaviour @property def si(self): """Return a copy with the physical unit in SI units.""" return self.__class__(self.physical.si) @property def cgs(self): """Return a copy with the physical unit in CGS units.""" return self.__class__(self.physical.cgs)
[docs] def decompose(self, bases=[]): """Generate a new `FunctionQuantity` with the physical unit decomposed. For details, see `~astropy.units.Quantity.decompose`. """ return self.__class__(self.physical.decompose(bases))
# ↓↓↓ methods overridden to add additional behaviour def __array_prepare__(self, obj, context=None): """Check that the ufunc can deal with a FunctionQuantity.""" # If no context is set, just return the input if context is None: # pragma: no cover return obj # Find out whether ufunc is supported function = context[0] if not (function in self._supported_ufuncs or all(arg.unit.physical_unit == dimensionless_unscaled for arg in context[1][:function.nin] if (hasattr(arg, 'unit') and hasattr(arg.unit, 'physical_unit')))): raise UnitTypeError("Cannot use function '{0}' with function " "quantities that are not dimensionless." .format(context[0].__name__)) return super().__array_prepare__(obj, context) def __quantity_subclass__(self, unit): if isinstance(unit, FunctionUnitBase): return self.__class__, True else: return super().__quantity_subclass__(unit)[0], False def _set_unit(self, unit): if not isinstance(unit, self._unit_class): # Have to take care of, e.g., (10*u.mag).view(u.Magnitude) try: # "or 'nonsense'" ensures `None` breaks, just in case. unit = self._unit_class(function_unit=unit or 'nonsense') except Exception: raise UnitTypeError( "{0} instances require {1} function units" .format(type(self).__name__, self._unit_class.__name__) + ", so cannot set it to '{0}'.".format(unit)) self._unit = unit # ↓↓↓ methods overridden to change behaviour def __mul__(self, other): if self.unit.physical_unit == dimensionless_unscaled: return self._function_view * other raise UnitTypeError("Cannot multiply function quantities which " "are not dimensionless with anything.") def __truediv__(self, other): if self.unit.physical_unit == dimensionless_unscaled: return self._function_view / other raise UnitTypeError("Cannot divide function quantities which " "are not dimensionless by anything.") def __rtruediv__(self, other): if self.unit.physical_unit == dimensionless_unscaled: return self._function_view.__rdiv__(other) raise UnitTypeError("Cannot divide function quantities which " "are not dimensionless into anything.") def _comparison(self, other, comparison_func): """Do a comparison between self and other, raising UnitsError when other cannot be converted to self because it has different physical unit, and returning NotImplemented when there are other errors.""" try: # will raise a UnitsError if physical units not equivalent other_in_own_unit = self._to_own_unit(other, check_precision=False) except UnitsError as exc: if self.unit.physical_unit != dimensionless_unscaled: raise exc try: other_in_own_unit = self._function_view._to_own_unit( other, check_precision=False) except Exception: raise exc except Exception: return NotImplemented return comparison_func(other_in_own_unit) def __eq__(self, other): try: return self._comparison(other, self.value.__eq__) except UnitsError: return False def __ne__(self, other): try: return self._comparison(other, self.value.__ne__) except UnitsError: return True def __gt__(self, other): return self._comparison(other, self.value.__gt__) def __ge__(self, other): return self._comparison(other, self.value.__ge__) def __lt__(self, other): return self._comparison(other, self.value.__lt__) def __le__(self, other): return self._comparison(other, self.value.__le__) # Ensure Quantity methods are used only if they make sense. def _wrap_function(self, function, *args, **kwargs): if function in self._supported_functions: return super()._wrap_function(function, *args, **kwargs) # For dimensionless, we can convert to regular quantities. if all(arg.unit.physical_unit == dimensionless_unscaled for arg in (self,) + args if (hasattr(arg, 'unit') and hasattr(arg.unit, 'physical_unit'))): args = tuple(getattr(arg, '_function_view', arg) for arg in args) return self._function_view._wrap_function(function, *args, **kwargs) raise TypeError("Cannot use method that uses function '{0}' with " "function quantities that are not dimensionless." .format(function.__name__))