Source code for openmdao.utils.units

"""
Classes and functions to support unit conversion.

The module provides a basic set of predefined physical quantities
in its built-in library; however, it also supports generation of
personal libararies which can be saved and reused.
This module is based on the PhysicalQuantities module
in Scientific Python, by Konrad Hinsen. Modifications by
Justin Gray.
"""

from __future__ import division, print_function


import sys

import re
import os.path
from collections import OrderedDict

from six import iteritems
from six.moves import zip
from six.moves.configparser import RawConfigParser as ConfigParser

# pylint: disable=E0611, F0401
from math import floor, pi


####################################
# Class Definitions
####################################


[docs]class NumberDict(OrderedDict): """ Dictionary storing numerical values. An instance of this class acts like an array of numbers with generalized (non-integer) indices. A value of zero is assumed for undefined entries. NumberDict instances support addition and subtraction with other NumberDict instances, and multiplication and division by scalars. """
[docs] def __getitem__(self, item): """ Get the item, or 0. Parameters ---------- item : key key to get the item Returns ------- int value of the given key """ try: return dict.__getitem__(self, item) except KeyError: return 0
def __coerce__(self, other): """ Change other dict to NumberDicts. Parameters ---------- other : Dict the dict instance to be coerced Returns ------- NumberDict new NumberDict with keys/values from original """ if isinstance(other, dict): other = NumberDict(other) return self, other def __add__(self, other): """ Add another NumberDict to myself. Parameters ---------- other : NumberDict the other NumberDict Instance Returns ------- NumberDict new NumberDict with self+other values """ sum_dict = NumberDict() for k, v in iteritems(self): sum_dict[k] = v for k, v in iteritems(other): sum_dict[k] = sum_dict[k] + v return sum_dict def __sub__(self, other): """ Add another NumberDict from myself. Parameters ---------- other : NumberDict the other NumberDict Instance Returns ------- NumberDict new NumberDict instance, with self-other values """ sum_dict = NumberDict() for k, v in iteritems(self): sum_dict[k] = v for k, v in iteritems(other): sum_dict[k] = sum_dict[k] - v return sum_dict def __rsub__(self, other): """ Add subtract myself from another NumberDict. Parameters ---------- other : NumberDict the other NumberDict Instance Returns ------- NumberDict new NumberDict instance, with other-self values """ sum_dict = NumberDict() for k, v in iteritems(other): sum_dict[k] = v for k, v in iteritems(self): sum_dict[k] = sum_dict[k] - v return sum_dict def __mul__(self, other): """ Multiply myself by another NumberDict. Parameters ---------- other : NumberDict the other NumberDict Instance Returns ------- NumberDict new NumberDict instance, with other*self values """ new = NumberDict() for key, value in iteritems(self): new[key] = other * value return new __rmul__ = __mul__ def __div__(self, other): """ Divide myself by another NumberDict. Parameters ---------- other : int value to divide by Returns ------- NumberDict new NumberDict instance, with self/other values """ new = NumberDict() for key, value in iteritems(self): new[key] = value / other return new __truediv__ = __div__ # for python 3 def __repr__(self): """ Return a string deceleration of myself. Parameters ---------- other : NumberDict the other NumberDict Instance Returns ------- str str representation for the creation of this NumberDict """ return repr(dict(self))
[docs]class PhysicalUnit(object): """ Physical unit. A physical unit is defined by a name (possibly composite), a scaling factor, and the exponentials of each of the SI base units that enter into it. Units can be multiplied, divided, and raised to integer powers. Attributes ---------- _names : dict or str A dictionary mapping each name component to its associated integer power (e.g., C{{'m': 1, 's': -1}}) for M{m/s}). As a shorthand, a string may be passed which is assigned an implicit power 1. _factor : float A scaling factor. _powers : list of int The integer powers for each of the nine base units. _offset : float An additive offset to the base unit (used only for temperatures) """
[docs] def __init__(self, names, factor, powers, offset=0): """ Initialize all attributes. Parameters ---------- names : dict or str A dictionary mapping each name component to its associated integer power (e.g., C{{'m': 1, 's': -1}}) for M{m/s}). As a shorthand, a string may be passed which is assigned an implicit power 1. factor : float A scaling factor. powers : list of int The integer powers for each of the nine base units. offset : float An additive offset to the base unit (used only for temperatures). """ if isinstance(names, str): self._names = NumberDict(((names, 1),)) else: self._names = names self._factor = float(factor) self._offset = float(offset) self._powers = powers
def __repr__(self): """ Get the string representation of this unit. Returns ------- str str representation of how to instantiate this PhysicalUnit """ return 'PhysicalUnit(%s,%s,%s,%s)' % (self._names, self._factor, self._powers, self._offset) def __str__(self): """ Convert myself to string. Returns ------- str str representation of a PhysicalUnit """ return '<PhysicalUnit ' + self.name() + '>' def __lt__(self, other): """ Compare myself to other. Parameters ---------- other : PhysicalUnit The other physical unit to be compared to Returns ------- bool self._factor < other._factor """ if self._powers != other._powers or self._offset != other._offset: raise TypeError('Incompatible units') return self._factor < other._factor def __gt__(self, other): """ Compare myself to other. Parameters ---------- other : PhysicalUnit The other physical unit to be compared to Returns ------- bool self._factor > other._factor """ if self._powers != other._powers: raise TypeError('Incompatible units') return self._factor > other._factor def __eq__(self, other): """ Test for equality. Parameters ---------- other : PhysicalUnit The other physical unit to be compared to Returns ------- bool true if _factor, _offset, and _powers all match """ return (self._factor == other._factor and self._offset == other._offset and self._powers == other._powers) def __mul__(self, other): """ Multiply myself by other. Parameters ---------- other : PhysicalUnit The other physical unit to be compared to Returns ------- PhysicalUnit new PhysicalUnit instance representing the product of two units """ if self._offset != 0 or (isinstance(other, PhysicalUnit) and other._offset != 0): raise TypeError("cannot multiply units with non-zero offset") if isinstance(other, PhysicalUnit): return PhysicalUnit(self._names + other._names, self._factor * other._factor, [a + b for a, b in zip(self._powers, other._powers)]) else: return PhysicalUnit(self._names + {str(other): 1}, self._factor * other, self._powers, self._offset * other) __rmul__ = __mul__ def __div__(self, other): """ Divide myself by other. Parameters ---------- other : PhysicalUnit The other physical unit to be operated on Returns ------- PhysicalUnit new PhysicalUnit instance representing the self/other """ if self._offset != 0 or (isinstance(other, PhysicalUnit) and other._offset != 0): raise TypeError("cannot divide units with non-zero offset") if isinstance(other, PhysicalUnit): return PhysicalUnit(self._names - other._names, self._factor / other._factor, [a - b for (a, b) in zip(self._powers, other._powers)]) else: return PhysicalUnit(self._names + {str(other): -1}, self._factor / float(other), self._powers) __truediv__ = __div__ # for python 3 def __rdiv__(self, other): """ Divide other by myself. Parameters ---------- other : PhysicalUnit The other physical unit to be operated on Returns ------- PhysicalUnit new PhysicalUnit instance representing the other/self """ return PhysicalUnit({str(other): 1} - self._names, float(other) / self._factor, [-x for x in self._powers]) __rtruediv__ = __rdiv__ def __pow__(self, other): """ Raise myself to a power. Parameters ---------- other : float or int power to raise self by Returns ------- PhysicalUnit new PhysicalUnit of self^other """ if self._offset != 0: raise TypeError("cannot exponentiate units with non-zero offset") if isinstance(other, int): return PhysicalUnit(other * self._names, pow(self._factor, other), [x * other for x in self._powers]) if isinstance(other, float): inv_exp = 1. / other rounded = int(floor(inv_exp + 0.5)) if abs(inv_exp - rounded) < 1.e-10: if all([x % rounded == 0 for x in self._powers]): f = self._factor**other p = [x / rounded for x in self._powers] if all([x % rounded == 0 for x in self._names.values()]): names = self._names / rounded else: names = NumberDict() if f != 1.: names[str(f)] = 1 for x, name in zip(p, _UNIT_LIB.base_names): names[name] = x return PhysicalUnit(names, f, p) raise TypeError('Only integer and inverse integer exponents allowed')
[docs] def in_base_units(self): """ Return the base unit equivalent of this unit. Returns ------- PhysicalUnit the equivalent base unit """ num = '' denom = '' for unit, power in zip(_UNIT_LIB.base_names, self._powers): if power < 0: denom = denom + '/' + unit if power < -1: denom = denom + '**' + str(-power) elif power > 0: num = num + '*' + unit if power > 1: num = num + '**' + str(power) if len(num) == 0: num = '1' else: num = num[1:] return _find_unit(num + denom)
[docs] def conversion_tuple_to(self, other): """ Compute the tuple of (factor, offset) for conversion. Parameters ---------- other : PhysicalUnit Another unit. Returns ------- Tuple with two floats The conversion factor and offset from this unit to another unit. """ if self._powers != other._powers: raise TypeError('Incompatible units') # let (s1,d1) be the conversion tuple from 'self' to base units # (ie. (x+d1)*s1 converts a value x from 'self' to base units, # and (x/s1)-d1 converts x from base to 'self' units) # and (s2,d2) be the conversion tuple from 'other' to base units # then we want to compute the conversion tuple (S,D) from # 'self' to 'other' such that (x+D)*S converts x from 'self' # units to 'other' units # the formula to convert x from 'self' to 'other' units via the # base units is (by definition of the conversion tuples): # ( ((x+d1)*s1) / s2 ) - d2 # = ( (x+d1) * s1/s2) - d2 # = ( (x+d1) * s1/s2 ) - (d2*s2/s1) * s1/s2 # = ( (x+d1) - (d1*s2/s1) ) * s1/s2 # = (x + d1 - d2*s2/s1) * s1/s2 # thus, D = d1 - d2*s2/s1 and S = s1/s2 factor = self._factor / other._factor offset = self._offset - (other._offset * other._factor / self._factor) return (factor, offset)
[docs] def is_compatible(self, other): """ Check for compatibility with another unit. Parameters ---------- other : PhysicalUnit Another unit. Returns ------- bool indicates if two units are compatible """ return self._powers == other._powers
[docs] def is_dimensionless(self): """ Dimensionless PQ. Returns ------- bool indicates if this is dimensionless """ return not any(self._powers)
[docs] def is_angle(self): """ Check if this PQ is an Angle. Returns ------- bool indicates if this an angle type """ return (self._powers[_UNIT_LIB.base_types['angle']] == 1 and sum(self._powers) == 1)
[docs] def set_name(self, name): """ Set the name. Parameters ---------- name : str the name """ self._names = NumberDict() self._names[name] = 1
[docs] def name(self): """ Compute the name of this unit. Returns ------- str str representation of the unit """ num = '' denom = '' for unit, power in iteritems(self._names): if power < 0: denom = denom + '/' + unit if power < -1: denom = denom + '**' + str(-power) elif power > 0: num = num + '*' + unit if power > 1: num = num + '**' + str(power) if len(num) == 0: num = '1' else: num = num[1:] return num + denom
#################################### # Module Functions #################################### def _new_unit(name, factor, powers): """ Create new Unit. Parameters ---------- name : str The name of the new unit factor : float conversion factor to base units powers : [int, ...] power of base units """ _UNIT_LIB.unit_table[name] = PhysicalUnit(name, factor, powers)
[docs]def add_offset_unit(name, baseunit, factor, offset, comment=''): """ Adding Offset Unit. Parameters ---------- name : str The name of the unit baseunit : str or instance of PhysicalUnit The unit upon which this offset unit is based. factor : str The scaling factor used to define the new unit w.r.t. baseunit offset : float zero offset for new unit comment : str optional comment to describe unit """ if isinstance(baseunit, str): baseunit = _find_unit(baseunit) # else, baseunit should be a instance of PhysicalUnit # names, factor, powers, offset=0 unit = PhysicalUnit(baseunit._names, baseunit._factor * factor, baseunit._powers, offset) unit.set_name(name) if name in _UNIT_LIB.unit_table: if (_UNIT_LIB.unit_table[name]._factor != unit._factor or _UNIT_LIB.unit_table[name]._powers != unit._powers): raise KeyError("Unit %s already defined with " % name + "different factor or powers") _UNIT_LIB.unit_table[name] = unit _UNIT_LIB.set('units', name, unit) if comment: _UNIT_LIB.help.append((name, comment, unit))
[docs]def add_unit(name, unit, comment=''): """ Adding Unit. Parameters ---------- name : str The name of the unit being added. For example: 'Hz' unit : str definition of the unit w.r.t. some other unit. For example: '1/s' comment : str optional comment to describe unit """ if comment: _UNIT_LIB.help.append((name, comment, unit)) if isinstance(unit, str): unit = eval(unit, {'__builtins__': None, 'pi': pi}, _UNIT_LIB.unit_table) unit.set_name(name) if name in _UNIT_LIB.unit_table: if (_UNIT_LIB.unit_table[name]._factor != unit._factor or _UNIT_LIB.unit_table[name]._powers != unit._powers): raise KeyError("Unit %s already defined with " % name + "different factor or powers") _UNIT_LIB.unit_table[name] = unit _UNIT_LIB.set('units', name, unit)
_UNIT_LIB = ConfigParser() def _do_nothing(string): """ Make the ConfigParser case sensitive. Defines an optionxform for the units configparser that does nothing, resulting in a case-sensitive parser. Parameters ---------- string : str The string to be transformed for the ConfigParser Returns ------- str The same string that was given as a parameter. """ return string _UNIT_LIB.optionxform = _do_nothing
[docs]def import_library(libfilepointer): """ Import a units library, replacing any existing definitions. Parameters ---------- libfilepointer : file new library file to work with Returns ------- ConfigParser newly updated units library for the module """ global _UNIT_LIB global _UNIT_CACHE _UNIT_CACHE = {} _UNIT_LIB = ConfigParser() _UNIT_LIB.optionxform = _do_nothing # New in Python 3.2: read_file() replaces readfp(). if sys.version_info >= (3, 2): _UNIT_LIB.read_file(libfilepointer) else: _UNIT_LIB.readfp(libfilepointer) required_base_types = ['length', 'mass', 'time', 'temperature', 'angle'] _UNIT_LIB.base_names = list() # used to is_angle() and other base type checking _UNIT_LIB.base_types = dict() _UNIT_LIB.unit_table = dict() _UNIT_LIB.prefixes = dict() _UNIT_LIB.help = list() for prefix, factor in _UNIT_LIB.items('prefixes'): factor, comma, comment = factor.partition(',') _UNIT_LIB.prefixes[prefix] = float(factor) base_list = [0] * len(_UNIT_LIB.items('base_units')) for i, (unit_type, name) in enumerate(_UNIT_LIB.items('base_units')): _UNIT_LIB.base_types[unit_type] = i powers = list(base_list) powers[i] = 1 # print '%20s'%unit_type, powers # cant use add_unit because no base units exist yet _new_unit(name, 1, powers) _UNIT_LIB.base_names.append(name) # test for required base types missing = [utype for utype in required_base_types if utype not in _UNIT_LIB.base_types] if missing: raise ValueError('Not all required base type were present in the' ' config file. missing: %s, at least %s required' % (missing, required_base_types)) # Explicit unitless 'unit'. _new_unit('unitless', 1, list(base_list)) _update_library(_UNIT_LIB) return _UNIT_LIB
[docs]def update_library(filename): """ Update units in current library from `filename`. Parameters ---------- filename : string or file Source of units configuration data. """ if isinstance(filename, basestring): inp = open(filename, 'rU') else: inp = filename try: cfg = ConfigParser() cfg.optionxform = _do_nothing # New in Python 3.2: read_file() replaces readfp(). if sys.version_info >= (3, 2): cfg.read_file(inp) else: cfg.readfp(inp) _update_library(cfg) finally: inp.close()
def _update_library(cfg): """ Update library from :class:`ConfigParser` `cfg`. Parameters ---------- cfg : ConfigParser ConfigParser loaded with unit_lib.ini data """ retry1 = set() for name, unit in cfg.items('units'): data = [item.strip() for item in unit.split(',')] if len(data) == 2: unit, comment = data try: add_unit(name, unit, comment) except NameError: retry1.add((name, unit, comment)) elif len(data) == 4: factor, baseunit, offset, comment = data try: add_offset_unit(name, baseunit, float(factor), float(offset), comment) except NameError: retry1.add((name, baseunit, float(factor), float(offset), comment)) else: raise ValueError('Unit %r definition %r has invalid format', name, unit) retry_count = 0 last_retry_count = -1 while last_retry_count != retry_count and retry1: last_retry_count = retry_count retry_count = 0 retry2 = retry1.copy() for data in retry2: if len(data) == 3: name, unit, comment = data try: add_unit(name, unit, comment) retry1.remove(data) except NameError: retry_count += 1 else: try: name, factor, baseunit, offset, comment = data add_offset_unit(name, factor, baseunit, offset, comment) retry1.remove(data) except NameError: retry_count += 1 if retry1: raise ValueError('The following units were not defined because they' ' could not be resolved as a function of any other' ' defined units:%s' % [x[0] for x in retry1]) _UNIT_CACHE = {} def _find_unit(unit): """ Find unit helper function. Parameters ---------- unit : str str representing the desired unit Returns ------- PhysicalUnit The actual unit object """ if isinstance(unit, str): name = unit.strip() try: unit = _UNIT_CACHE[name] except KeyError: try: unit = eval(name, {'__builtins__': None}, _UNIT_LIB.unit_table) except Exception: # This unit might include prefixed units that aren't in the # unit_table. We must parse them ALL and add them to the # unit_table. # First character of a unit is always alphabet or $. # Remaining characters may include numbers. regex = re.compile('[A-Z,a-z]{1}[A-Z,a-z,0-9]*') for item in regex.findall(name): # check if this was a compound unit, so each # substring might be a unit try: eval(item, {'__builtins__': None}, _UNIT_LIB.unit_table) except Exception: # maybe is a prefixed unit then # check for single letter prefix before unit if(item[0] in _UNIT_LIB.prefixes and item[1:] in _UNIT_LIB.unit_table): add_unit(item, _UNIT_LIB.prefixes[item[0]] * _UNIT_LIB.unit_table[item[1:]]) # check for double letter prefix before unit elif(item[0:2] in _UNIT_LIB.prefixes and item[2:] in _UNIT_LIB.unit_table): add_unit(item, _UNIT_LIB.prefixes[item[0:2]] * _UNIT_LIB.unit_table[item[2:]]) # no prefixes found, unknown unit else: return None # raise ValueError("no unit named '%s' is defined" # % item) unit = eval(name, {'__builtins__': None}, _UNIT_LIB.unit_table) _UNIT_CACHE[name] = unit if not isinstance(unit, PhysicalUnit): return None return unit
[docs]def valid_units(unit): """ Return whether the given units are vaild. Parameters ---------- unit : str String representation of the units. Returns ------- bool True for valid, False for invalid. """ return _find_unit(unit) is not None
[docs]def conversion_to_base_units(units): """ Get the offset and scaler to convert from given units to base units. Parameters ---------- units : str String representation of the units. Returns ------- float Offset to get to default unit: m (length), s(time), etc. float Mult. factor to get to default unit: m (length), s(time), etc. """ if not units: # dimensionless return 0., 1. unit = _find_unit(units) return unit._offset, unit._factor
[docs]def is_compatible(old_units, new_units): """ Check whether units are compatible in terms of base units. e.g., m/s is compatible with ft/hr Parameters ---------- old_units : str original units as a string. new_units : str or None new units to return the value in; if None, return in standard units. Returns ------- bool whether the units are compatible. """ if not old_units and not new_units: # dimensionless return True old_unit = _find_unit(old_units) new_unit = _find_unit(new_units) return old_unit.is_compatible(new_unit)
[docs]def get_conversion(old_units, new_units): """ Return conversion factor and offset between old and new units. Parameters ---------- old_units : str original units as a string. new_units : str new units to return the value in. Returns ------- (float, float) Conversion factor and offset """ new_physical_units = _find_unit(new_units) if new_physical_units is None: raise RuntimeError("Cannot convert to new units: %s" % str(new_units)) return _find_unit(old_units).conversion_tuple_to(new_physical_units)
[docs]def convert_units(val, old_units, new_units=None): """ Take a given quantity and return in different units. Parameters ---------- val : float value in original units. old_units : str or None original units as a string or None. new_units : str or None new units to return the value in or None. Returns ------- float value in new units. """ if not old_units or not new_units: # one side has no units return val old_unit = _find_unit(old_units) if new_units: new_unit = _find_unit(new_units) else: new_unit = old_unit.in_base_units() (factor, offset) = old_unit.conversion_tuple_to(new_unit) return (val + offset) * factor
# Load in the default unit library file_path = open(os.path.join(os.path.dirname(__file__), 'unit_library.ini')) with file_path as default_lib: import_library(default_lib) if __name__ == '__main__': for returned, expected in [ (conversion_to_base_units('cm'), (0., 1.0e-2)), (conversion_to_base_units('km'), (0., 1.0e3)), (convert_units(3.0, 'mm'), (3.0e-3)), (convert_units(3.0, 'mm', 'cm'), (3.0e-1)), (convert_units(100, 'degC', 'degF'), (212.)) ]: print(returned, 'should be', expected)