python/cpython · error · ValueError

The second value in the tuple must be composed of integers i

Error message

The second value in the tuple must be composed of integers in the range 0 through 9.

What it means

In Decimal's tuple/list constructor, the second element must be an iterable of Python ints each in 0..9 — these are the coefficient digits. Anything else (an int outside 0-9, a string digit like '5', a None) raises this ValueError. Leading zeros are skipped, but every element must still be a valid digit.

Source

Thrown at Lib/_pydecimal.py:579

                raise ValueError("Invalid sign.  The first value in the tuple "
                                 "should be an integer; either 0 for a "
                                 "positive number or 1 for a negative number.")
            self._sign = value[0]
            if value[2] == 'F':
                # infinity: value[1] is ignored
                self._int = '0'
                self._exp = value[2]
                self._is_special = True
            else:
                # process and validate the digits in value[1]
                digits = []
                for digit in value[1]:
                    if isinstance(digit, int) and 0 <= digit <= 9:
                        # skip leading zeros
                        if digits or digit != 0:
                            digits.append(digit)
                    else:
                        raise ValueError("The second value in the tuple must "
                                         "be composed of integers in the range "
                                         "0 through 9.")
                if value[2] in ('n', 'N'):
                    # NaN: digits form the diagnostic
                    self._int = ''.join(map(str, digits))
                    self._exp = value[2]
                    self._is_special = True
                elif isinstance(value[2], int):
                    # finite number: digits give the coefficient
                    self._int = ''.join(map(str, digits or [0]))
                    self._exp = value[2]
                    self._is_special = False
                else:
                    raise ValueError("The third value in the tuple must "
                                     "be an integer, or one of the "
                                     "strings 'F', 'n', 'N'.")
            return self

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Map string digits to ints: digits = tuple(int(c) for c in '142')
2. Validate each digit with isinstance(d, int) and 0 <= d <= 9 before constructing
3. If you have the number as text, skip the tuple entirely: Decimal('1.42')

Example fix

// before
d = Decimal((0, tuple('142'), 0))  # strings -> ValueError

// after
d = Decimal((0, tuple(int(c) for c in '142'), 0))  # Decimal('142')

def valid_digits(digits) -> bool:
    return all(isinstance(d, int) and 0 <= d <= 9 for d in digits)

# digits = tuple(int(c) for c in digit_str) if digit_str.isascii() and digit_str.isdigit() else digits

def is_digit_tuple(digits) -> bool:
    return hasattr(digits, '__iter__') and all(
        isinstance(d, int) and not isinstance(d, bool) and 0 <= d <= 9
        for d in digits
    )

try:
    d = Decimal((sign, digits, exp))
except ValueError as e:
    if 'second value' in str(e):
        digits = tuple(int(c) for c in ''.join(map(str, digits)))
        d = Decimal((sign, digits, exp))

When it happens

Trigger: Decimal((0, (1, 25), 0)) (25 out of range); Decimal((0, '142', 0)) (string characters, not ints); Decimal((0, (1, None), 0)); Decimal((0, (), 'F')) is fine (empty digits with 'F'), but Decimal((0, (-1,), 0)) fails.

Common situations: Converting a digit string to a digits tuple without mapping to int: tuple('142') gives ('1','4','2'); deserialized triples where digits were JSON-encoded as strings; passing a single int instead of an iterable of digits.

Related errors

• Invalid tuple size in creation of Decimal from list or tuple
• Invalid sign. The first value in the tuple should be an int
• The third value in the tuple must be an integer, or one of t
• argument must be a multiple of 32, with a maximum of {IEEE_C
• skip_file_prefixes must be a tuple of strs.

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/6fb5486227033e52. Report an issue: GitHub.