Python: Make this code more compact?

Question

How can I get rid of the excessive repetition in this code?

Code: http://pastebin.com/13e2nWM9

The program calculates equations of motion (SUVAT Equations) based on data provided by the user.

The section I refer to is:

while True:
        a = raw_input("What is the value of a? Make sure it is in standard units, however, do not include the unit.")
        try:
            float(a)
            print "a is " + str(a) + " ms^-2"
            break
        except:
            print"You must enter a number. Don't include units!"

This is repeated many times, save for the variable 'a' and the unit which changes when the block is repeated.

Many thanks.

Answer 1

Here is one option, put the following function definition at the top of your module:

def get_float(name, units):
    prompt = "What is the value of {0}? Make sure it is in standard units, however, do not include the unit.".format(name)
    while True:
        val = raw_input(prompt)
        try:
            val = float(val)
            print '{0} is {1} {2}'.format(name, val, units)
            return val
        except Exception:
            print "You must enter a number. Don't include units!"

Here is an example of how you could use it, the following code could replace everything from line 72 to 100:

name_units_pairs = [('v', 'ms^-1'), ('a', 'ms^-2'), ('t', 's'),]
vals = {}
for name, units in name_units_pairs:
    vals[name] = get_float(name, units)
u = vals['v'] - vals['a'] * vals['t']

Answer 2

Do not use raw excepts, and encapsulate the tests, that is all. So instead of

while True:
        a = raw_input("What is the value of a? Make sure it is in standard units, however, do not include the unit.")
        try:
            float(a)
            print "a is " + str(a) + " ms^-2"
            break
        except:
            print"You must enter a number. Don't include units!"

do

a = my_input(valuename='a', unit='m^-2', unitformat=float)

and do the tests (and prompts) in my_input.

my_input may look something like:

def my_input(valuename, unit, unitformat=float):
  while True:
    val = raw_input("What is the value of %s? Make sure it is in standard units"+
                    "(%s), however, do not include the unit." % (valuename, unit))
    try:
        unitformat(val)
    except ValueError:
        print"You must enter a number. Don't include units!"
    else:
        print "%s is %s %s" % (valuename, val, unit)
        return val