[Python] string format a Decimal instance using an underscore as a thousands separator?

I can easily do this for floats using an f-string like this:

x = float(123456789.123456)
print(f"{x:_f}")


prints 123_456_789.123456 exactly as expected.

But if try the same technique for a Decimal

from decimal import Decimal
x = Decimal("123456789.123456")
print(f"{x:_f}")


this code crashes with ValueError: invalid format string

What?

Does Decimal only partly support Python's Format Specification Mini-Language?

Is this a known bug with Decimal?

This is especially strange because Decimal does support underscore as a thousands separator when parsing FROM a string:

from decimal import Decimal
x = Decimal("123_456_789.123456")
print(f"{x:f}")


prints 123456789.123456 exactly as expected.

Is this there another way that I can do this?

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