NumberRange step validation

[azmeuk]

As mentioned in #654, it could be interesting to add a step argument to the NumberRange validator. This way it could validate some discrete values. A value x should be accepted if min <= x <= max and x - min % step == 0.

For instance NumberRange(min=10, max=20, step=3) would only accept values in [10, 13, 16, 19]

[davidism]

I think this would only work reliably for ints though, in which case the following should also work:

if int(value) == value and value not in range(min, max, step):
    raise ValidationError(...)

... # original min/max only checks

[azmeuk]

I can imagine cases with FloadField, DateField or MonthField too.

[davidism]

I don't think step can work (or at least be accurate) for float, but I'm not 100% sure. Dates aren't numbers, that would probably require a different validator that used something like dateutil.rrule. Months are ints, so this should work for that.

[whb07]

It essentially ends up being the issue that everyone has with floats and precision/truncation, right?

I could imagine something naive being

step = "0.01"
_, step_val = step.split(".")
value = "1.123"
_, decimal = value.split(".")
if len(decimal) >  len(step_val):
    raise Error

After that initial check, its a modulo check for the step sizing validation.

[azmeuk]

6 years later, I cannot think of a real world use case for this. Let us close this and reopen it if someone comes up with an example.