Unit balancing

[AbrahamLincolnIllinois@yahoo.com]

Greetings!

I am working with a researcher who would be very happy if he could
include units in his calculations. Then, if his complicated expression
didn't result in "kg/yr" the program would stop and point out his
error.

Does Python (or SciPy or ..) offer this feature?

Thanks for your help.


Abraham

[Tim Chase]

Re: Unit balancing

I am working with a researcher who would be very happy if he

could include units in his calculations. Then, if his
complicated expression didn't result in "kg/yr" the program
would stop and point out his error.
>
Does Python (or SciPy or ..) offer this feature?

Well, it's a bit of a hack, but you could try something like

############### ############### #############
class InvalidUnits(Ex ception): pass

class Unit(object):
def __init__(self, value, units = ''):
self.value = value
self.units = units
def __sub__(self, other):
if isinstance(othe r, Unit):
if self.units <other.units:
raise InvalidUnits
return Unit(self.value - other.value, self.units)
return Unit(self.value - other, self.units)
def __add__(self, other):
if isinstance(othe r, Unit):
if self.units <other.units:
raise InvalidUnits
return Unit(self.value + other.value, self.units)
return Unit(self.value + other, self.units)
def __mul__(self, other):
if isinstance(othe r, Unit):
return Unit(self.value * other.value,
"(%s)%s" % (self.units, other.units))
else:
return Unit(self.value * other, self.units)
def __div__(self, other):
if isinstance(othe r, Unit):
return Unit(self.value / other.value,
"%s/%s" % (self.units, other.units))
else:
return Unit(self.value / other, self.units)
def __radd__(self, other): return self.__add__(ot her)
def __rsub__(self, other): return self.__sub__(ot her)
def __rmul__(self, other): return self.__mul__(ot her)
def __rdiv__(self, other): return self.__div__(ot her)
def __repr__(self):
return '%i %s' % (self.value, self.units)
def __str__(self): return repr(self)
############### ############### ############### ###############

which allows you to do things like

distance = Unit(80, 'm')
print "Distance: %s" % distance
time = Unit(2, 'h')
print "Time: %s" % time
speed = distance/time
print "Speed: %s" % speed
speed = 3 * speed
print "Speed: %s" % speed
print "Error:",
# can't add dissimilar units
print distance + time



I'm sure there are loads of other edge cases one would want to
consider, such as analyzing and trimming redundant units, but
that should give a pretaste of what could be done.

-tkc

[Simon Brunning]

Re: Unit balancing

On 13 Sep 2006 07:47:41 -0700, AbrahamLincolnI llinois@yahoo.c om
<AbrahamLincoln Illinois@yahoo. comwrote:

I am working with a researcher who would be very happy if he could
include units in his calculations. Then, if his complicated expression
didn't result in "kg/yr" the program would stop and point out his
error.

This what you were looking for?

<http://home.tiscali.be/be052320/Unum.html>

--
Cheers,
Simon B,
simon@brunningo nline.net

[Claudio Grondi]

Re: Unit balancing

AbrahamLincolnI llinois@yahoo.c om wrote:

Greetings!
>
I am working with a researcher who would be very happy if he could
include units in his calculations. Then, if his complicated expression
didn't result in "kg/yr" the program would stop and point out his
error.
>
Does Python (or SciPy or ..) offer this feature?
>
Thanks for your help.
>
>
Abraham
>

I mean I run one time already into a Python library or a class which was
designed to handle such things as this request is common to many
researcher.
Sorry, don't have any link at my fingertips or even an idea where to
look after it, so Googling or waiting until someone else using such a
tool posts here is all I can offer.

Inbetween Frink is maybe an option?

http://futureboy.homeip.net/frinkdocs/

Claudio Grondi

[AbrahamLincolnIllinois@yahoo.com]

Re: Unit balancing

Thanks, all.

We will investigate Unum.


Abraham