Performing arithmetic on floating point values of different sizes

Question

My code does not run as I would expect if one float variable has 5 digits, others have 4, and an arithmetical operation is performed on them. For example:

def capacity(self):

    mmax = self.mmax.get()
    current = self.current.get()
    mmin = self.mmin.get()

    flag = False

    if flag is False:
        if mmax.isdigit() and mmin.isdigit() and current.isdigit():
            capacity = float(100 * ((float(current) - float(mmin)) / (float(mmax) - float(mmin))))
            if mmin <= current <= mmax and 0 <= capacity <= 100:
                flag = True
            else:
                self.result = str("Please ensure the values entered correspond to the correct value.")
        else:
            self.result = str("Please enter only positive integers.")

    if flag is True:
        self.result = "Capacity: %2.2f" % capacity + '%'

If mmax = 10000, current = 5000, and mmin = 1000, self.result = str("Please ensure...").
If mmax = 9999, current = 5000, and mmin = 1000, self.result = str("Capacity: 44.45%).

What's going on here/ how can I overcome this problem?

Answer 1

I'm guessing that mmin and current and mmax are strings. In which case, this expression:

if mmin <= current <= mmax and 0 <= capacity <= 100:

... Is doing a lexicographical comparison on the values. This is different from a numerical comparison: for example, "5000" < "10000" evaluates to False because "5" is larger than "1".

Convert your values to numbers before doing comparisons on them.

if mmax.isdigit() and mmin.isdigit() and current.isdigit():
    mmax = float(mmax)
    current = float(current)
    mmin = float(mmin)

    capacity = float(100 * ... #etc

Or

if float(mmin) <= float(current) <= float(mmax) and 0 <= capacity <= 100: