Currency with 3 decimal digits in python

I have the following code which compares the input value that comes as a string with the one the function constracts. Basically checks the if the number the user enters is correct. The function works but only for 2 decimal points but the user is allowed to enter 2 to 4 decimal digits... How can I construct the right value?

def check_currency(self, amount):
        amount = amount.replace("+", "")
        amount = amount.replace("-", "")
        sInput = amount.replace(",", ".")
        locale.setlocale(locale.LC_ALL, self.LANG)
        result = locale.currency(float(sInput), symbol=False, grouping=True)
        if (amount == result):
            return True
        else:
            return False

PS: The self.LANG get the respective value based on the system that the code runs on.

Solution

You aren't missing anything. locale.currency formats numbers according to the values in the dict returned by locale.localeconv() and that's what it's supposed to do. Naturally, 'frac_digits' is typically 2 since... well... you know.

Regarding what to do:

First, you can check 'int_frac_digits' in localeconv() - maybe it's good enough for you.

If not, since locale.currency is located in a Python source module, you can rig... I mean, override its logic. Looking at the source, the simplest method appears to be to replace locale.localeconv() with a wrapper.

Be wary though since such a change will be global. If you don't want it to affect other code using locale, alter local copies of the entities (or the entire module) or make a changed entity e.g. require an additional parameter to behave differently.

On a conceptual note: locale is actually correct - for its purpose - in not allowing to alter the representation. Its task is to format information of a few types according to the local convention - so whatever culture you user pertains to, they will see information in the way they are used to. If you alter the format in any way - that wouldn't any longer be "the local convention"! In fact, by requiring 3 decimal digits, you are already making assumptions about the local convention - which may not stand. E.g. in a decent share of currencies, even small sums can numerically be in the thousands.