Here goes the variables' parent class
#===============================================================================
# Variable quantities with units
# Written by Konrad Hinsen <hin...@cnrs-orleans.fr>
# with contributions from Greg Ward
# last revision: 2007-5-25
# Revised for SIAM-PFM by Paul Williams <william...@ornl.gov>
#
#===============================================================================
class VariableQuantity( object ):
'''
Variable quantities with units.
This module provides a data type that represents a physical
quantity together with its units. It is possible to add and
subtract these quantities if the units are compatible, and
a quantity can be converted to another compatible unit.
Multiplication, subtraction, and raising to integer powers
is allowed without restriction, and the result will have
the correct unit. A quantity can be raised to a non-integer
power only if the result can be represented by integer powers
of the base units.
The values of physical constants are taken from the 1986
recommended values from CODATA. Other conversion factors
(e.g. for British units) come from various sources.
VariableQuantity instances allow addition, subtraction,
multiplication, and division with each other as well as
multiplication, division, and exponentiation with numbers.
Addition and subtraction check that the units of the two operands
are compatible and return the result in the units of the first
operand. A limited set of mathematical functions (from module
Numeric) is applicable as well:
- sqrt: equivalent to exponentiation with 0.5.
- sin, cos, tan: applicable only to objects whose unit is
compatible with 'rad'.
See the documentation of the VariableQuantities module for a list
of the available units.
Here is an example on usage:
>>> from PhysicalVariables import VariableQuantity as p # short
hand
>>> distance1 = p('10 m')
>>> distance2 = p('10 km')
>>> total = distance1 + distance2
>>> total
VariableQuantity(10010.0,'m')
>>> total.convertToUnit('km')
>>> total.getValue()
10.01
>>> total.getUnitName()
'km'
>>> total = total.inBaseUnits()
>>> total
VariableQuantity(10010.0,'m')
>>>
>>> t = p(314159., 's')
>>> # convert to days, hours, minutes, and second:
>>> t2 = t.inUnitsOf('d','h','min','s')
>>> t2_print = ' '.join([str(i) for i in t2])
>>> t2_print
'3.0 d 15.0 h 15.0 min 59.0 s'
>>>
>>> e = p('2.7 Hartree*Nav')
>>> e.convertToUnit('kcal/mol')
>>> e
VariableQuantity(1694.2757596034764,'kcal/mol')
>>> e = e.inBaseUnits()
>>> str(e)
'7088849.77818 kg*m**2/s**2/mol'
>>>
>>> freeze = p('0 degC')
>>> freeze = freeze.inUnitsOf ('degF')
>>> str(freeze)
'32.0 degF'
>>>
'''
def __init__( self, *args ):
'''
There are two constructor calling patterns:
1. VariableQuantity(value, unit), where value is any
number
and unit is a string defining the unit
2. VariableQuantity(value_with_unit), where
value_with_unit
is a string that contains both the value and the unit,
i.e. '1.5 m/s'. This form is provided for more convenient
interactive use.
@param args: either (value, unit) or (value_with_unit,)
@type args: (number, C{str}) or (C{str},)
'''
if len( args )==2:
self.value=args[0]
self.unit=_findUnit( args[1] )
else:
s=string.strip( args[0] )
match=VariableQuantity._number.match( s )
if match is None:
raise TypeError( 'No number found' )
self.value=string.atof( match.group( 0 ) )
self.unit=_findUnit( s[len( match.group( 0 ) ):] )
_number=re.compile( '[+-]?[0-9]+(\\.[0-9]*)?([eE][+-]?[0-9]+)?' )
def __str__( self ):
return str( self.value )+' '+self.unit.name()
def __repr__( self ):
return ( self.__class__.__name__+'('+`self.value`+','+
`self.unit.name()`+')' )
def _sum( self, other, sign1, sign2 ):
if not isVariableQuantity( other ):
raise TypeError( 'Incompatible types' )
new_value=sign1*self.value+\
sign2*other.value*other.unit.conversionFactorTo
( self.unit )
return self.__class__( new_value, self.unit )
def __add__( self, other ):
return self._sum( other, 1, 1 )
__radd__=__add__
def __sub__( self, other ):
return self._sum( other, 1,-1 )
def __rsub__( self, other ):
return self._sum( other,-1, 1 )
def __cmp__( self, other ):
diff=self._sum( other, 1,-1 )
return cmp( diff.value, 0 )
def __mul__( self, other ):
if not isVariableQuantity( other ):
return self.__class__( self.value*other, self.unit )
value=self.value*other.value
unit=self.unit*other.unit
if unit.isDimensionless():
return value*unit.factor
else:
return self.__class__( value, unit )
__rmul__=__mul__
def __div__( self, other ):
if not isVariableQuantity( other ):
return self.__class__( self.value/other, self.unit )
value=self.value/other.value
unit=self.unit/other.unit
if unit.isDimensionless():
return value*unit.factor
else:
return self.__class__( value, unit )
def __rdiv__( self, other ):
if not isVariableQuantity( other ):
return self.__class__( other/self.value, pow
( self.unit,-1 ) )
value=other.value/self.value
unit=other.unit/self.unit
if unit.isDimensionless():
return value*unit.factor
else:
return self.__class__( value, unit )
def __pow__( self, other ):
if isVariableQuantity( other ):
raise TypeError( 'Exponents must be dimensionless' )
return self.__class__( pow( self.value, other ), pow
( self.unit, other ) )
def __rpow__( self, other ):
raise TypeError( 'Exponents must be dimensionless' )
def __abs__( self ):
return self.__class__( abs( self.value ), self.unit )
def __pos__( self ):
return self
def __neg__( self ):
return self.__class__( -self.value, self.unit )
def __nonzero__( self ):
return self.value!=0
def convertToUnit( self, unit ):
"""
Change the unit and adjust the value such that
the combination is equivalent to the original one. The new
unit
must be compatible with the previous unit of the object.
@param unit: a unit
@type unit: C{str}
@raise TypeError: if the unit string is not a know unit or a
unit incompatible with the current one
"""
unit=_findUnit( unit )
self.value=_convertValue ( self.value, self.unit, unit )
self.unit=unit
def inUnitsOf( self, *units ):
"""
Express the quantity in different units. If one unit is
specified, a new VariableQuantity object is returned that
expresses the quantity in that unit. If several units
are specified, the return value is a tuple of
VariableObject instances with with one element per unit such
that the sum of all quantities in the tuple equals the the
original quantity and all the values except for the last one
are integers. This is used to convert to irregular unit
systems like hour/minute/second.
@param units: one or several units
@type units: C{str} or sequence of C{str}
@returns: one or more physical quantities
@rtype: L{VariableQuantity} or C{tuple} of L{VariableQuantity}
@raises TypeError: if any of the specified units are not
compatible
with the original unit
"""
units=map( _findUnit, units )
if len( units )==1:
unit=units[0]
value=_convertValue ( self.value, self.unit, unit )
return self.__class__( value, unit )
else:
units.sort()
result=[]
value=self.value
unit=self.unit
for i in range( len( units )-1,-1,-1 ):
value=value*unit.conversionFactorTo( units[i] )
if i==0:
rounded=value
else:
rounded=_round( value )
result.append( self.__class__( rounded, units[i] ) )
value=value-rounded
unit=units[i]
return tuple( result )
# Contributed by Berthold Hoellmann
def inBaseUnits( self ):
"""
@returns: the same quantity converted to base units,
i.e. SI units in most cases
@rtype: L{VariableQuantity}
"""
new_value=self.value*self.unit.factor
num=''
denom=''
for i in xrange( 9 ):
unit=_base_names[i]
power=self.unit.powers[i]
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 self.__class__( new_value, num+denom )
def isCompatible ( self, unit ):
"""
@param unit: a unit
@type unit: C{str}
@returns: C{True} if the specified unit is compatible with the
one of the quantity
@rtype: C{bool}
"""
unit=_findUnit ( unit )
return self.unit.isCompatible ( unit )
def getValue( self ):
"""Return value (float) of physical quantity (no unit)."""
return self.value
def setValue( self, value ):
'''
Set nominal constant value: typically the mean or median
@param value: nominal constant value of xLPRVariable
@type value: float or int
'''
self.value=value
def getUnitName( self ):
"""Return unit (string) of physical quantity."""
return self.unit.name()
def sqrt( self ):
return pow( self, 0.5 )
def sin( self ):
if self.unit.isAngle():
return N.sin( self.value*\
self.unit.conversionFactorTo( _unit_table
['rad'] ) )
else:
raise TypeError( 'Argument of sin must be an angle' )
def cos( self ):
if self.unit.isAngle():
return N.cos( self.value*\
self.unit.conversionFactorTo( _unit_table
['rad'] ) )
else:
raise TypeError( 'Argument of cos must be an angle' )
def tan( self ):
if self.unit.isAngle():
return N.tan( self.value*\
self.unit.conversionFactorTo( _unit_table
['rad'] ) )
else:
raise TypeError( 'Argument of tan must be an angle' )
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.
"""
def __init__( self, names, factor, powers, offset = 0 ):
"""
@param names: 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.
@type names: C{dict} or C{str}
@param factor: a scaling factor
@type factor: C{float}
@param powers: the integer powers for each of the nine base
units
@type powers: C{list} of C{int}
@param offset: an additive offset to the base unit (used only
for
temperatures)
@type offset: C{float}
"""
if type( names )==type( '' ):
self.names=NumberDict()
self.names[names]=1
else:
self.names=names
self.factor=factor
self.offset=offset
self.powers=powers
def __repr__( self ):
return '<PhysicalUnit '+self.name()+'>'
__str__=__repr__
def __cmp__( self, other ):
if self.powers!=other.powers:
raise TypeError( 'Incompatible units' )
return cmp( self.factor, other.factor )
def __mul__( self, other ):
if self.offset!=0 or ( isPhysicalUnit ( other ) and
other.offset!=0 ):
raise TypeError( "cannot multiply units with non-zero
offset" )
if isPhysicalUnit( other ):
return PhysicalUnit( self.names+other.names,
self.factor*other.factor,
map( lambda a, b: a+b,
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 ):
if self.offset!=0 or ( isPhysicalUnit ( other ) and
other.offset!=0 ):
raise TypeError( "cannot divide units with non-zero
offset" )
if isPhysicalUnit( other ):
return PhysicalUnit( self.names-other.names,
self.factor/other.factor,
map( lambda a, b: a-b,
self.powers, other.powers ) )
else:
return PhysicalUnit( self.names+{str( other ):-1},
self.factor/other, self.powers )
def __rdiv__( self, other ):
if self.offset!=0 or ( isPhysicalUnit ( other ) and
other.offset!=0 ):
raise TypeError( "cannot divide units with non-zero
offset" )
if isPhysicalUnit( other ):
return PhysicalUnit( other.names-self.names,
other.factor/self.factor,
map( lambda a, b: a-b,
other.powers, self.powers ) )
else:
return PhysicalUnit( {str( other ): 1}-self.names,
other/self.factor,
map( lambda x:-x, self.powers ) )
def __pow__( 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 ),
map( lambda x, p = other: x*p,
self.powers ) )
if isinstance( other, float ):
inv_exp=1./other
rounded=int( N.floor( inv_exp+0.5 ) )
if abs( inv_exp-rounded )<1.0e-10:
if reduce( lambda a, b: a and b,
map( lambda x, e = rounded: x%e==0,
self.powers ) ):
f=pow( self.factor, other )
p=map( lambda x, p = rounded: x/p, self.powers )
if reduce( lambda a, b: a and b,
map( lambda x, e = rounded: x%e==0,
self.names.values() ) ):
names=self.names/rounded
else:
names=NumberDict()
if f!=1.:
names[str( f )]=1
for i in range( len( p ) ):
names[_base_names[i]]=p[i]
return PhysicalUnit( names, f, p )
else:
raise TypeError( 'Illegal exponent' )
raise TypeError( 'Only integer and inverse integer exponents
allowed' )
def conversionFactorTo( self, other ):
"""
@param other: another unit
@type other: L{PhysicalUnit}
@returns: the conversion factor from this unit to another unit
@rtype: C{float}
@raises TypeError: if the units are not compatible
"""
if self.powers!=other.powers:
raise TypeError( 'Incompatible units' )
if self.offset!=other.offset and self.factor!=other.factor:
raise TypeError( ( 'Unit conversion (%s to %s) cannot be
expressed '+
'as a simple multiplicative factor' )%\
( self.name(), other.name() ) )
return self.factor/other.factor
def conversionTupleTo( self, other ): # added 1998/09/29 GPW
"""
@param other: another unit
@type other: L{PhysicalUnit}
@returns: the conversion factor and offset from this unit to
another unit
@rtype: (C{float}, C{float})
@raises TypeError: if the units are not compatible
"""
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 )
def isCompatible ( self, other ): # added 1998/10/01 GPW
"""
@param other: another unit
@type other: L{PhysicalUnit}
@returns: C{True} if the units are compatible, i.e. if the
powers of
the base units are the same
@rtype: C{bool}
"""
return self.powers==other.powers
def isDimensionless( self ):
return not reduce( lambda a, b: a or b, self.powers )
def isAngle( self ):
return self.powers[7]==1 and \
reduce( lambda a, b: a+b, self.powers )==1
def setName( self, name ):
self.names=NumberDict()
self.names[name]=1
def name( self ):
num=''
denom=''
for unit in self.names.keys():
power=self.names[unit]
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
# Type checks
def isPhysicalUnit( x ):
"""
@param x: an object
@type x: any
@returns: C{True} if x is a L{PhysicalUnit}
@rtype: C{bool}
"""
return hasattr( x, 'factor' ) and hasattr( x, 'powers' )
def isVariableQuantity( x ):
"""
@param x: an object
@type x: any
@returns: C{True} if x is a L{VariableQuantity}
@rtype: C{bool}
"""
return hasattr( x, 'value' ) and hasattr( x, 'unit' )
# Helper functions
def _findUnit( unit ):
if type( unit )==type( '' ):
name=string.strip( unit )
unit=eval( name, _unit_table )
for cruft in ['__builtins__', '__args__']:
try: del _unit_table[cruft]
except: pass
if not isPhysicalUnit( unit ):
raise TypeError( str( unit )+' is not a unit' )
return unit
def _round( x ):
if N.greater( x, 0. ):
return N.floor( x )
else:
return N.ceil( x )
def _convertValue ( value, src_unit, target_unit ):
( factor, offset )=src_unit.conversionTupleTo( target_unit )
return ( value+offset )*factor
# SI unit definitions
_base_names=['m', 'kg', 's', 'A', 'K', 'mol', 'cd', 'rad', 'sr']
_base_units=[( 'm', PhysicalUnit( 'm', 1., [1, 0, 0, 0, 0, 0, 0, 0,
0] ) ),
( 'g', PhysicalUnit( 'g', 0.001, [0, 1, 0, 0, 0, 0, 0,
0, 0] ) ),
( 's', PhysicalUnit( 's', 1., [0, 0, 1, 0, 0, 0, 0, 0,
0] ) ),
( 'A', PhysicalUnit( 'A', 1., [0, 0, 0, 1, 0, 0, 0, 0,
0] ) ),
( 'K', PhysicalUnit( 'K', 1., [0, 0, 0, 0, 1, 0, 0, 0,
0] ) ),
( 'mol', PhysicalUnit( 'mol', 1., [0, 0, 0, 0, 0, 1, 0,
0, 0] ) ),
( 'cd', PhysicalUnit( 'cd', 1., [0, 0, 0, 0, 0, 0, 1,
0, 0] ) ),
( 'rad', PhysicalUnit( 'rad', 1., [0, 0, 0, 0, 0, 0, 0,
1, 0] ) ),
( 'sr', PhysicalUnit( 'sr', 1., [0, 0, 0, 0, 0, 0, 0,
0, 1] ) ),
]
_prefixes=[( 'Y', 1.e24 ),
( 'Z', 1.e21 ),
( 'E', 1.e18 ),
( 'P', 1.e15 ),
( 'T', 1.e12 ),
( 'G', 1.e9 ),
( 'M', 1.e6 ),
( 'k', 1.e3 ),
( 'h', 1.e2 ),
( 'da', 1.e1 ),
( 'd', 1.e-1 ),
( 'c', 1.e-2 ),
( 'm', 1.e-3 ),
( 'mu', 1.e-6 ),
( 'n', 1.e-9 ),
( 'p', 1.e-12 ),
( 'f', 1.e-15 ),
( 'a', 1.e-18 ),
( 'z', 1.e-21 ),
( 'y', 1.e-24 ),
]
_unit_table={}
for unit in _base_units:
_unit_table[unit[0]]=unit[1]
_help=[]
def _addUnit( name, unit, comment = '' ):
if _unit_table.has_key( name ):
raise KeyError, 'Unit '+name+' already defined'
if comment:
_help.append( ( name, comment, unit ) )
if type( unit )==type( '' ):
unit=eval( unit, _unit_table )
for cruft in ['__builtins__', '__args__']:
try: del _unit_table[cruft]
except: pass
unit.setName( name )
_unit_table[name]=unit
def _addPrefixed( unit ):
_help.append( 'Prefixed units for %s:'%unit )
_prefixed_names=[]
for prefix in _prefixes:
name=prefix[0]+unit
_addUnit( name, prefix[1]*_unit_table[unit] )
_prefixed_names.append( name )
_help.append( ', '.join( _prefixed_names ) )
# SI derived units; these automatically get prefixes
_help.append( 'SI derived units; these automatically get prefixes:\n'+
\
', '.join( [prefix+' (%.0E)'%value for prefix, value in
_prefixes] )+\
'\n' )
_unit_table['kg']=PhysicalUnit( 'kg', 1., [0, 1, 0, 0, 0, 0, 0, 0,
0] )
_addUnit( 'Hz', '1/s', 'Hertz' )
_addUnit( 'N', 'm*kg/s**2', 'Newton' )
_addUnit( 'Pa', 'N/m**2', 'Pascal' )
_addUnit( 'J', 'N*m', 'Joule' )
_addUnit( 'W', 'J/s', 'Watt' )
_addUnit( 'C', 's*A', 'Coulomb' )
_addUnit( 'V', 'W/A', 'Volt' )
_addUnit( 'F', 'C/V', 'Farad' )
_addUnit( 'ohm', 'V/A', 'Ohm' )
_addUnit( 'S', 'A/V', 'Siemens' )
_addUnit( 'Wb', 'V*s', 'Weber' )
_addUnit( 'T', 'Wb/m**2', 'Tesla' )
_addUnit( 'H', 'Wb/A', 'Henry' )
_addUnit( 'lm', 'cd*sr', 'Lumen' )
_addUnit( 'lx', 'lm/m**2', 'Lux' )
_addUnit( 'Bq', '1/s', 'Becquerel' )
_addUnit( 'Gy', 'J/kg', 'Gray' )
_addUnit( 'Sv', 'J/kg', 'Sievert' )
del _unit_table['kg']
for unit in _unit_table.keys():
_addPrefixed( unit )
# Fundamental constants
_help.append( 'Fundamental constants:' )
_unit_table['pi']=math.pi
_addUnit( 'c', '299792458.*m/s', 'speed of light' )
_addUnit( 'mu0', '4.e-7*pi*N/A**2', 'permeability of vacuum' )
_addUnit( 'eps0', '1/mu0/c**2', 'permittivity of vacuum' )
_addUnit( 'Grav', '6.67259e-11*m**3/kg/s**2', 'gravitational
constant' )
_addUnit( 'hplanck', '6.6260755e-34*J*s', 'Planck constant' )
_addUnit( 'hbar', 'hplanck/(2*pi)', 'Planck constant / 2pi' )
_addUnit( 'e', '1.60217733e-19*C', 'elementary charge' )
_addUnit( 'me', '9.1093897e-31*kg', 'electron mass' )
_addUnit( 'mp', '1.6726231e-27*kg', 'proton mass' )
_addUnit( 'Nav', '6.0221367e23/mol', 'Avogadro number' )
_addUnit( 'k', '1.380658e-23*J/K', 'Boltzmann constant' )
# Time units
_help.append( 'Time units:' )
_addUnit( 'min', '60*s', 'minute' )
_addUnit( 'h', '60*min', 'hour' )
_addUnit( 'd', '24*h', 'day' )
_addUnit( 'wk', '7*d', 'week' )
# added by ptw 12/17/2009
_addUnit( 'mon', '2629800*s', 'month' )
_addUnit( 'yr', '365.25*d', 'year' )
# Length units
_help.append( 'Length units:' )
_addUnit( 'inch', '2.54*cm', 'inch' )
_addUnit( 'ft', '12*inch', 'foot' )
_addUnit( 'yd', '3*ft', 'yard' )
_addUnit( 'mi', '5280.*ft', '(British) mile' )
_addUnit( 'nmi', '1852.*m', 'Nautical mile' )
_addUnit( 'Ang', '1.e-10*m', 'Angstrom' )
_addUnit( 'lyr', 'c*yr', 'light year' )
_addUnit( 'Bohr', '4*pi*eps0*hbar**2/me/e**2', 'Bohr radius' )
# Area units
_help.append( 'Area units:' )
_addUnit( 'ha', '10000*m**2', 'hectare' )
_addUnit( 'acres', 'mi**2/640', 'acre' )
_addUnit( 'b', '1.e-28*m', 'barn' )
# Volume units
_help.append( 'Volume units:' )
_addUnit( 'l', 'dm**3', 'liter' )
_addUnit( 'dl', '0.1*l', 'deci liter' )
_addUnit( 'cl', '0.01*l', 'centi liter' )
_addUnit( 'ml', '0.001*l', 'milli liter' )
_addUnit( 'tsp', '4.92892159375*ml', 'teaspoon' )
_addUnit( 'tbsp', '3*tsp', 'tablespoon' )
_addUnit( 'floz', '2*tbsp', 'fluid ounce' )
_addUnit( 'cup', '8*floz', 'cup' )
_addUnit( 'pt', '16*floz', 'pint' )
_addUnit( 'qt', '2*pt', 'quart' )
_addUnit( 'galUS', '4*qt', 'US gallon' )
_addUnit( 'galUK', '4.54609*l', 'British gallon' )
# Mass units
_help.append( 'Mass units:' )
_addUnit( 'amu', '1.6605402e-27*kg', 'atomic mass units' )
_addUnit( 'oz', '28.349523125*g', 'ounce' )
_addUnit( 'lb', '16*oz', 'pound' )
_addUnit( 'ton', '2000*lb', 'ton' )
# Force units
_help.append( 'Force units:' )
_addUnit( 'dyn', '1.e-5*N', 'dyne (cgs unit)' )
# Energy units
_help.append( 'Energy units:' )
_addUnit( 'erg', '1.e-7*J', 'erg (cgs unit)' )
_addUnit( 'eV', 'e*V', 'electron volt' )
_addUnit( 'Hartree', 'me*e**4/16/pi**2/eps0**2/hbar**2', 'Wavenumbers/
inverse cm' )
_addUnit( 'Ken', 'k*K', 'Kelvin as energy unit' )
_addUnit( 'cal', '4.184*J', 'thermochemical calorie' )
_addUnit( 'kcal', '1000*cal', 'thermochemical kilocalorie' )
_addUnit( 'cali', '4.1868*J', 'international calorie' )
_addUnit( 'kcali', '1000*cali', 'international kilocalorie' )
_addUnit( 'Btu', '1055.05585262*J', 'British thermal unit' )
_addPrefixed( 'eV' )
# Power units
_help.append( 'Power units:' )
_addUnit( 'hp', '745.7*W', 'horsepower' )
# Pressure units
_help.append( 'Pressure units:' )
_addUnit( 'bar', '1.e5*Pa', 'bar (cgs unit)' )
_addUnit( 'atm', '101325.*Pa', 'standard atmosphere' )
_addUnit( 'torr', 'atm/760', 'torr = mm of mercury' )
_addUnit( 'psi', '6894.757749*Pa', 'pounds per square inch' )
# Angle units
_help.append( 'Angle units:' )
_addUnit( 'deg', 'pi*rad/180', 'degrees' )
_help.append( 'Temperature units:' )
# Temperature units -- can't use the 'eval' trick that _addUnit
provides
# for degC and degF because you can't add units
kelvin=_findUnit ( 'K' )
_addUnit ( 'degR', '(5./9.)*K', 'degrees Rankine' )
_addUnit ( 'degC', PhysicalUnit ( None, 1.0, kelvin.powers, 273.15 ),
'degrees Celcius' )
_addUnit ( 'degF', PhysicalUnit ( None, 5./9., kelvin.powers,
459.67 ),
'degree Fahrenheit' )
del kelvin
def description():
"""Return a string describing all available units."""
s='' # collector for description text
for entry in _help:
if isinstance( entry, basestring ):
# headline for new section
s+='\n'+entry+'\n'
elif isinstance( entry, tuple ):
name, comment, unit=entry
s+='%-8s %-26s %s\n'%( name, comment, unit )
else:
# impossible
raise TypeError, 'wrong construction of _help list'
return s
# add the description of the units to the module's doc string:
__doc__+='\n'+description()
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