[Tutor] Re: Please critique my temperature_conversion.py

[Andrei]

Dick Moores <rdm <at> rcblue.com> writes:

> from string import upper

Don't use the string module. Use string method instead, e.g. mystring.upper()
instead of string.upper(mystring).

> F_or_C = ""

As said by the previous poster, this isn't a very great name. I'd prefer
something like original_unit or from_unit.

> while (F_or_C != "F" and F_or_C != "C"):
>      t0 = raw_input("Enter temperature as 70F or 70 F or -12.47C: ")

I don't particulary like the name t0 neither. To me, this suggests "initial
time". Why not just call it e.g. temperature or even temp (although that
suggests something temporary).

>      F_or_C = upper(t0[-1]) # store the F or C and ensure upper case

If the user hits a space after the unit, this code won't recognise it. I'd
recommend stripping the input first.

>      t0 = t0[0:-1] #  strip entered temp of the F or C
>      t = t0 # get a string number to do the conversion calculation

Ah, but how do you know that it is a number? The user might have written
"kjanvkanvdf".

> if F_or_C == "F":
>      t = 5/9. * (float(t) - 32)

And here the lack of input validation will bite you. If t is now "kjanvkanvd",
the program will crash with a not particularly user-friendely error message.
It's better to validate the input using try-except and make sure that by the
time you end up in here, it's certainly a number.

>      t = round(t,2)
>      print (t0 + "F"), "is", (str(t) + "C")
<snip>

As already recommended, use format instrings instead. They're much clearer.

You didn't ask for them, but here are two other suggestions for improvements
anyway :)

- allow more than one conversion: run a potentially endless loop allowing the
user to convert a value and present her with a new prompt once the conversion is
done (or failed because of invalid input), so a new one can be done. A bit like
a very simple version of the Python interactive interpreter.

- add command line support, so it's possible to start e.g. "converttemp.py 32F"
and get the result in Celsius immediately, after which the program shuts itself
down.

Yours,

Andrei