TheAlgorithms/Python · error · ValueError

Non-octal value was passed to the function

Error message

Non-octal value was passed to the function

What it means

Raised by oct_to_decimal() in conversions/octal_to_decimal.py when the input string (after optional '-' sign and strip) is not composed solely of octal digits 0-7. The function first checks isdigit(), then verifies every char is in 0..7; failing either raises this ValueError. It exists to reject decimal-looking inputs such as '19' that contain the digits 8 or 9.

Source

Thrown at conversions/octal_to_decimal.py:67

        ...
    ValueError: Non-octal value was passed to the function
    >>> oct_to_decimal("")
    Traceback (most recent call last):
        ...
    ValueError: Empty string was passed to the function
    >>> oct_to_decimal("19")
    Traceback (most recent call last):
        ...
    ValueError: Non-octal value was passed to the function
    """
    oct_string = str(oct_string).strip()
    if not oct_string:
        raise ValueError("Empty string was passed to the function")
    is_negative = oct_string[0] == "-"
    if is_negative:
        oct_string = oct_string[1:]
    if not oct_string.isdigit() or not all(0 <= int(char) <= 7 for char in oct_string):
        raise ValueError("Non-octal value was passed to the function")
    decimal_number = 0
    for char in oct_string:
        decimal_number = 8 * decimal_number + int(char)
    if is_negative:
        decimal_number = -decimal_number
    return decimal_number


if __name__ == "__main__":
    from doctest import testmod

    testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Sanitize the input before calling: keep only chars in '01234567' (plus optional leading '-') or reject early.
2. If the value is decimal, convert it the other way (decimal_to_octal) or fix the upstream data producer.
3. Strip a '0o'/'0O' prefix yourself before calling, since this function does not accept it.
4. Wrap the call in try/except ValueError if the input is untrusted and show a validation message.

Example fix

# before
oct_to_decimal('19')  # ValueError: Non-octal value was passed to the function

# after
valid = set('01234567')
s = '19'
if not s.lstrip('-').isdigit() or any(c not in valid for c in s.lstrip('-')):
    raise ValueError(f'{s!r} is not an octal string')
oct_to_decimal(s)

def is_octal_string(s: str) -> bool:
    s = str(s).strip().lstrip('-')
    return s.isdigit() and all(0 <= int(c) <= 7 for c in s)

if not is_octal_string(user_value):
    raise ValueError(f'{user_value!r} is not a valid octal string')
oct_to_decimal(user_value)

def is_octal_string(s: str) -> bool:
    s = str(s).strip().lstrip('-')
    return s.isdigit() and all(c in '01234567' for c in s)

try:
    oct_to_decimal(raw)
except ValueError as e:
    if 'Non-octal' in str(e):
        show_field_error('value must contain only digits 0-7')
    else:
        raise

When it happens

Trigger: Calling oct_to_decimal('19'), oct_to_decimal('8'), oct_to_decimal('abc') (fails isdigit), or any string containing '8'/'9' after a leading '-' is removed. Whitespace is stripped first, so ' 18 ' also triggers it.

Common situations: Feeding user input from a form or file directly into the converter; passing a decimal literal as a string because the source data was decimal, not octal; accidentally passing '0o17' (the 'o' fails isdigit).

Related errors

• Not a Valid Octal Number
• Expected a string as input
• Empty string was passed to the function
• Invalid 'from_type' value: {from_type!r} Supported values a
• Invalid 'to_type' value: {to_type!r}. Supported values are:

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/c4c826c1103b7906. Report an issue: GitHub.