"""
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 libraries which can be saved and reused.
This module is based on the PhysicalQuantities module
in Scientific Python, by Konrad Hinsen.
It has been modified by Justin Gray for integration in OpenMDAO 2.2 and by the CoSApp team
for integration in CoSApp (mainly remove Python 2 support).
"""
import os.path
import re
from collections import OrderedDict
from configparser import _UNSET, DEFAULTSECT, RawConfigParser
from math import floor, pi
from numbers import Number
from typing import Any, Dict, List, Optional, Tuple, Union
# TODO could it be more interesting to merge this with the PhysicalQuantities package of
# https://github.com/juhasch/PhysicalQuantities - unfortunately this package as lots of others don't
# have a easy way to get the convertion tuple (offset, factor)...
# TODO this code is not the cleanest nor the robustest
####################################
# Class Definitions
####################################
[docs]
class UnitError(Exception):
"""Raised if units are incompatible or unknown.
Parameters
----------
message : str
Error message
Attributes
----------
message : str
Error message
"""
def __init__(self, message: str):
"""Instantiate a error object from the error descriptive message.
Parameters
----------
message : str
Error message
"""
self.message = message
[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.
"""
def __getitem__(self, item: str) -> int:
"""
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: Dict[str, float]) -> Tuple['NumberDict', 'NumberDict']:
"""
Change other dict to NumberDicts.
Parameters
----------
other : Dict
the dict instance to be coerced
Returns
-------
Tuple[NumberDict, NumberDict]
old and new NumberDict with keys/values from original
"""
if isinstance(other, dict):
other = NumberDict(other)
return self, other
def __add__(self, other: 'NumberDict') -> 'NumberDict':
"""
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 self.items():
sum_dict[k] = v
for k, v in other.items():
sum_dict[k] = sum_dict[k] + v
return sum_dict
def __sub__(self, other: 'NumberDict') -> 'NumberDict':
"""
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 self.items():
sum_dict[k] = v
for k, v in other.items():
sum_dict[k] = sum_dict[k] - v
return sum_dict
def __rsub__(self, other: 'NumberDict') -> 'NumberDict':
"""
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 other.items():
sum_dict[k] = v
for k, v in self.items():
sum_dict[k] = sum_dict[k] - v
return sum_dict
def __mul__(self, other: int) -> 'NumberDict':
"""
Multiply myself by other.
Parameters
----------
other : int
value to multiply by
Returns
-------
NumberDict
new NumberDict instance, with other*self values
"""
new = NumberDict()
for key, value in self.items():
new[key] = other * value
return new
__rmul__ = __mul__
def __div__(self, other: int) -> 'NumberDict':
"""
Divide myself by other.
Parameters
----------
other : int
value to divide by
Returns
-------
NumberDict
new NumberDict instance, with self/other values
"""
new = NumberDict()
for key, value in self.items():
new[key] = value / other
return new
__truediv__ = __div__ # for python 3
def __repr__(self) -> str:
"""
Return a string deceleration of myself.
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)
"""
def __init__(self, names: Union[str, Dict[str, int]], factor: float, powers: List[int],
offset: float=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),)) # type: NumberDict
else:
self._names = NumberDict(names) # type: NumberDict
self._factor = float(factor) # type: float
self._offset = float(offset) # type: float
self._powers = powers # type: List[int]
def __repr__(self) -> str:
"""
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) -> str:
"""
Convert myself to string.
Returns
-------
str
str representation of a PhysicalUnit
"""
return '<PhysicalUnit ' + self.name() + '>'
def __lt__(self, other: 'PhysicalUnit') -> bool:
"""
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 UnitError(f"Unit {other.name()} is not compatible with {self.name()}.")
return self._factor < other._factor
def __gt__(self, other: 'PhysicalUnit') -> bool:
"""
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 UnitError(f"Unit {other.name()} is not compatible with {self.name()}.")
return self._factor > other._factor
def __eq__(self, other: 'PhysicalUnit') -> bool:
"""
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)
# TODO the case for other is a number seems wrong
def __mul__(self, other: Union['PhysicalUnit', int]) -> 'PhysicalUnit':
"""
Multiply myself by other.
Parameters
----------
other : PhysicalUnit or int
The other physical unit or the magnitude to be multiplied with
Returns
-------
PhysicalUnit
new PhysicalUnit instance representing the product of two units
"""
if abs(self._offset) > 1e-9 or (isinstance(other, PhysicalUnit) and
abs(other._offset) > 1e-9):
raise UnitError("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__
# TODO the case for other is a number seems wrong
def __div__(self, other: Union['PhysicalUnit', int]) -> 'PhysicalUnit':
"""
Divide myself by other.
Parameters
----------
other : PhysicalUnit or int
The other physical unit or magnitude to be divided by
Returns
-------
PhysicalUnit
new PhysicalUnit instance representing the self/other
"""
if abs(self._offset) > 1e-9 or (isinstance(other, PhysicalUnit) and
abs(other._offset) > 1e-9):
raise UnitError("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
# TODO this seems wrong
def __rdiv__(self, other: int) -> 'PhysicalUnit':
"""
Divide other by myself.
Parameters
----------
other : int
The other value to be divided by this unit
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: Union[int, float]) -> 'PhysicalUnit':
"""
Raise myself to a power.
Parameters
----------
other : float or int
power to raise self by
Returns
-------
PhysicalUnit
new PhysicalUnit of self^other
"""
if abs(self._offset) > 1e-9:
raise UnitError("cannot exponentiate units with non-zero offset")
if isinstance(other, int): # TODO something is wrong here
return PhysicalUnit(self._names * other, 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) -> 'PhysicalUnit':
"""
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: 'PhysicalUnit') -> Tuple[float, float]:
"""
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 UnitError(f"Unit {other.name()} is not compatible with {self.name()}.")
# 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: 'PhysicalUnit') -> bool:
"""
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) -> bool:
"""
Dimensionless PQ.
Returns
-------
bool
indicates if this is dimensionless
"""
return not any(self._powers)
[docs]
def is_angle(self) -> bool:
"""
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: str):
"""
Set the name.
Parameters
----------
name : str
the name
"""
self._names = NumberDict()
self._names[name] = 1
[docs]
def name(self) -> str:
"""
Compute the name of this unit.
Returns
-------
str
str representation of the unit
"""
num = ''
denom = ''
for unit, power in self._names.items():
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: str, factor: float, powers: List[int]) -> None:
"""
Create new PhysicalUnit and add it to the unit library.
Parameters
----------
name : str
The name of the new unit
factor : float
conversion factor to base units
powers : list of int
power of base units
"""
_UNIT_LIB.unit_table[name] = PhysicalUnit(name, factor, powers)
[docs]
def add_offset_unit(name: str, baseunit: Union[str, PhysicalUnit], factor: float, offset: float,
comment: str='') -> None:
"""
Adding Offset PhysicalUnit to the unit library.
Parameters
----------
name : str
The name of the unit
baseunit : str or PhysicalUnit
The unit upon which this offset unit is based.
factor : float
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: str, unit: str, comment: str = '') -> None:
"""
Adding PhysicalUnit from its name and string representation to the unit library.
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)
[docs]
class UnitConfigParser(RawConfigParser):
"""Customized configuration file parser to store physical units."""
def __init__(self, defaults=None, dict_type=OrderedDict, allow_no_value=False,
delimiters=('=', ':'), comment_prefixes=('#', ';'), inline_comment_prefixes=None,
strict=True, empty_lines_in_values=True, default_section=DEFAULTSECT,
interpolation=_UNSET):
super().__init__(defaults, dict_type, allow_no_value, delimiters=delimiters,
comment_prefixes=comment_prefixes,
inline_comment_prefixes=inline_comment_prefixes, strict=strict,
empty_lines_in_values=empty_lines_in_values,
default_section=default_section, interpolation=interpolation)
self.base_names = list() # type: List[str]
# used to is_angle() and other base type checking
self.base_types = dict() # type: Dict[str, int]
self.unit_table = dict()
self.prefixes = dict() # type: Dict[str, float]
self.help = list()
_UNIT_LIB = UnitConfigParser()
[docs]
def import_library(libfilepointer) -> UnitConfigParser:
"""
Import a units library, replacing any existing definitions.
Parameters
----------
libfilepointer : file
new library file to work with
Returns
-------
UnitConfigParser
newly updated units library for the module
"""
global _UNIT_LIB
global _UNIT_CACHE
_UNIT_CACHE = {}
_UNIT_LIB = UnitConfigParser()
_UNIT_LIB.read_file(libfilepointer)
required_base_types = ['length', 'mass', 'time', 'temperature', 'angle']
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: Union[str, Any]) -> None:
"""
Update units in current library from `filename`.
Parameters
----------
filename : string or file
Source of units configuration data.
"""
if isinstance(filename, str):
inp = open(filename, 'rU')
else:
inp = filename
try:
cfg = RawConfigParser()
cfg.optionxform = lambda s: s
cfg.read_file(inp)
_update_library(cfg)
finally:
inp.close()
def _update_library(cfg: RawConfigParser) -> None:
"""
Update library from :class:`RawConfigParser` `cfg`.
Parameters
----------
cfg : RawConfigParser
RawConfigParser 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(f"Unit {name!r} definition {unit!r} has invalid format")
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 = {} # type: Dict[str, PhysicalUnit]
def _find_unit(unit: Union[str, PhysicalUnit, None]) -> Optional[PhysicalUnit]:
"""
Find unit helper function.
Parameters
----------
unit : str or PhysicalUnit
str representing the desired unit
Returns
-------
PhysicalUnit or None
The actual unit object - None if not found
"""
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 (SyntaxError, NameError, TypeError):
# 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.
# Remaining characters may include numbers.
regex = re.compile(r"[A-z][A-z0-9]*")
if not regex.match(name):
return None
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 (SyntaxError, NameError, TypeError): # 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 is_valid_units(unit: Union[str, PhysicalUnit]) -> bool:
"""
Return whether the given units are valid.
Parameters
----------
unit : str or PhysicalUnit
Unit to test for.
Returns
-------
bool
True for valid, False for invalid.
"""
return _find_unit(unit) is not None
[docs]
def conversion_to_base_units(units: Union[str, PhysicalUnit]) -> Tuple[float, float]:
"""
Get the offset and scaler to convert from given units to base units.
Parameters
----------
units : str or PhysicalUnit
Unit or its representation.
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: Union[str, PhysicalUnit], new_units: Union[str, PhysicalUnit]) -> bool:
"""
Check whether units are compatible in terms of base units.
e.g., m/s is compatible with ft/hr
Parameters
----------
old_units : str or PhysicalUnit
original units
new_units : str or PhysicalUnit
new units to check compatibility with
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)
if old_unit is None or new_unit is None:
return False
return old_unit.is_compatible(new_unit)
[docs]
def get_conversion(old_units: Union[str, PhysicalUnit, None], new_units: Union[str, PhysicalUnit, None]) \
-> Optional[Tuple[float, float]]:
"""
Return conversion factor and offset between old and new units.
Parameters
----------
old_units : str or PhysicalUnit
original units
new_units : str or PhysicalUnit
new units to get the conversion from.
Returns
-------
(float, float) or None
Conversion factor and offset or None is no conversion available
"""
old_unit = _find_unit(old_units)
new_unit = _find_unit(new_units)
if old_unit is None or new_unit is None:
return None
else:
return old_unit.conversion_tuple_to(new_unit)
[docs]
def convert_units(val: float,
old_units: Union[str, PhysicalUnit, None] = None,
new_units: Union[str, PhysicalUnit, None] = None) -> float:
"""
Take a given quantity and return in different units.
If there is no current units or no target units, the original value is returned.
Parameters
----------
val : Number
value in original units.
old_units : str or PhysicalUnit or None
original units or None.
new_units : str or PhysicalUnit 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)
new_unit = _find_unit(new_units)
(factor, offset) = old_unit.conversion_tuple_to(new_unit)
return (val + offset) * factor
# Load in the default unit library
with open(os.path.join(os.path.dirname(__file__), 'unit_library.dat')) 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)
