QuantiPhy Eval — Computations with Physical Quantities

Author

Ken Kundert

Version

0.2.0

Released

2020-03-06

A companion to QuantiPhy, quantiphy_eval evaluates strings containing simple algebraic expressions that involve quantities. It returns a quantity. For example:

>>> from quantiphy_eval import evaluate

>>> average = evaluate('($1.2M + $1.3M)/2', '$')
>>> print(f'{average}')
$1.25M

>>> f_avg = evaluate('(122.317MHz + 129.349MHz)/2', 'Hz')
>>> print(f'{f_avg}')
125.83 MHz

With QuantiPhy the units do not survive operations, so you can specify the resolved units using the second argument. In fact, the second argument is passed to QuantiPhy as the model, which allows you to give the return value a name and description along with units, as demonstrated in the next example.

QuantiPhy Eval provides three constants built-in: pi, tau, and e. However, you can pass in additional constants:

>>> from quantiphy import Quantity

>>> my_constants = dict(
...     k = Quantity('k'),
...     q = Quantity('q'),
...     T = Quantity('25°C', scale='K'),
... )
>>> Vt = evaluate('k*T/q', 'Vt V thermal voltage', constants=my_constants)
>>> print(Vt.render(show_label='f'))
Vt = 25.693 mV -- thermal voltage

QuantiPhy Eval provides the following functions built-in: sin, cos, tan, sqrt, abs, trunc, round and sgn. However, you can pass in additional functions:

>>> def median(*args):
...    args = sorted(args)
...    l = len(args)
...    m = l//2
...    if l % 2:
...        return args[m]
...    return (args[m] + args[m-1])/2

>>> my_functions = dict(median=median)
>>> median_price = evaluate(
...     'median($636122, $749151, $706781)',
...     '$',
...     functions=my_functions
... )
>>> print(median_price.fixed(show_commas=True))
$706,781

QuantiPhy Eval provides rm_commas function for removing commas from an expression. This is used if your number contain commas. Simply stripping the commas it would prevent you from using multi-argument functions, however after removing the commas rm_commas also converts semicolons to commas. So the previous example could be rewritten as:

>>> from quantiphy_eval import evaluate, rm_commas

>>> median_price = evaluate(
...     rm_commas('median($636,122; $749,151; $706,781)'),
...     '$',
...     functions=my_functions
... )
>>> print(median_price.fixed(show_commas=True))
$706,781

Finally, QuantiPhy Eval supports comments. A # and anything that follows it to the end of the line is ignored:

>>> average_price = evaluate(
...     rm_commas('''
...         (
...             $636,122 +   # Zillow
...             $749,151 +   # Redfin
...             $706,781     # Trulia
...         )/3
...     '''),
...     '$'
... )
>>> print(average_price.fixed(show_commas=True, prec=2, strip_zeros=False))
$697,351.33

Releases

Latest development release:
Version: 0.2.0
Released: 2020-03-06
0.2 (2020-03-06):
  • rm_commas now converts semicolons to commas

  • support comments

0.1 (2020-03-05):
  • Add support for user-defined constants and functions.

  • add rm_commas function.

0.0 (2020-02-14):

Initial version.