Elegant list of conditions in Python

Question

I'm making a unit converting function for Python for fun.

This is my code, so far:

def UnitConverter(number,*units):
    if units == ("feet","inches"):
        return number*12
    elif units == ("ft","yd"):
        return number/3

You probably get the idea of how I'm having this work.

Because I'm obsessive about elegance, good code practice, and overall flow, I want to know what you coders think about this in general, in addition to my main question: How can I efficiently check for a list of permutations in an if statement?

Example: Is there an efficient way to make this work?

def UnitConverter(number,*units):
    if units == (("feet" or "foot" or "ft."),("inches" or "in" or "in.")):
        return number*12
    elif units == ("ft","yd"):
        return number/3

If not, is there a way to restructure my program such that someone can enter the three arguments number, unit1, unit2 in a way that on the coding end, I can effectively include all alternate spellings of each unit (feet,foot,ft,etc)?

I really value everyone's opinion.

Thanks!

Answer 1

I would pick a standard unit of length, let's say m. Then I would have a single dictionary that gives a factor for each other unit, and convert:

conversion_factors = {
    'foot': 0.3048,  # Google search '1 foot in m'
    'yard': 0.9144,
    # etc
}

def unit_convert(number, from_unit='m', to_unit='m'):
    m = number * conversion_factor[from_unit]
    return m / conversion_factor[to_unit]

For the synonyms (feet, ft, etc) you could make a second dictionary and lookup the canonical name in that first:

conversion_factors = { ... }  # as above

synonyms = {
    'feet': 'foot',
    'ft': 'foot',
    ...
}

def unit_convert(number, from_unit='m', to_unit='m'):
    from_unit = synonyms.get(from_unit, from_unit)
    to_unit = synonyms.get(to_unit, to_unit)
    # etc

...or just put them in the conversion_factors dictionary multiple times:

conversion_factors = {
    'foot': 0.3048,  # Google search '1 foot in m'
    'feet': 0.3048,
    'ft': 0.3048,
    'yard': 0.9144,
    # etc
}

Answer 2

Use sets.

foot_units = {"ft.", "feet", "foot"}

Then you can check ownership in the sets.

if(units[0] in foot_units):
   ...

Beyond this, make a conversion_factor dictionary that goes to a common conversion element. You can then coerce to your final after.

inches -> feet -> yards
inches -> feet -> feet

RemcoGerlich has a good solution for that step.

Answer 3

Perhaps something like the following, using the in operator which checks for containment:

def UnitConverter(number,*units):
    feet = {'feet', 'foot', 'ft.'}
    inches = {'inches', 'in', 'in.'}
    yards = {'yard', 'yd', 'yd.'}
    if units[0] in feet and units[1] in inches:
        return number*12
    elif units[0] in feet and units[1] in yards:
        return number/3