Method test_flags_irrelevant

Lib/test/test_decimal.py:3881–3945

(self)

class ContextFlags:

    def test_flags_irrelevant(self):
        # check that the result (numeric result + flags raised) of an
        # arithmetic operation doesn't depend on the current flags
        Decimal = self.decimal.Decimal
        Context = self.decimal.Context
        Inexact = self.decimal.Inexact
        Rounded = self.decimal.Rounded
        Underflow = self.decimal.Underflow
        Clamped = self.decimal.Clamped
        Subnormal = self.decimal.Subnormal

        def raise_error(context, flag):
            if self.decimal == C:
                context.flags[flag] = True
                if context.traps[flag]:
                    raise flag
            else:
                context._raise_error(flag)

        context = Context(prec=9, Emin = -425000000, Emax = 425000000,
                          rounding=ROUND_HALF_EVEN, traps=[], flags=[])

        # operations that raise various flags, in the form (function, arglist)
        operations = [
            (context._apply, [Decimal("100E-425000010")]),
            (context.sqrt, [Decimal(2)]),
            (context.add, [Decimal("1.23456789"), Decimal("9.87654321")]),
            (context.multiply, [Decimal("1.23456789"), Decimal("9.87654321")]),
            (context.subtract, [Decimal("1.23456789"), Decimal("9.87654321")]),
            ]

        # try various flags individually, then a whole lot at once
        flagsets = [[Inexact], [Rounded], [Underflow], [Clamped], [Subnormal],
                    [Inexact, Rounded, Underflow, Clamped, Subnormal]]

        for fn, args in operations:
            # find answer and flags raised using a clean context
            context.clear_flags()
            ans = fn(*args)
            flags = [k for k, v in context.flags.items() if v]

            for extra_flags in flagsets:
                # set flags, before calling operation
                context.clear_flags()
                for flag in extra_flags:
                    raise_error(context, flag)
                new_ans = fn(*args)

                # flags that we expect to be set after the operation
                expected_flags = list(flags)
                for flag in extra_flags:
                    if flag not in expected_flags:
                        expected_flags.append(flag)
                expected_flags.sort(key=id)

                # flags we actually got
                new_flags = [k for k,v in context.flags.items() if v]
                new_flags.sort(key=id)