TheAlgorithms/Python · error · ValueError

Not a Valid Octal Number

Error message

Not a Valid Octal Number

What it means

Raised by octal_to_hex() in conversions/octal_to_hexadecimal.py when any character of the input (after optional '0o' prefix removal) is not in '01234567'. This catches digits 8/9 as well as letters like 'A' — note hex letters are invalid here because the input is expected to be octal, not hex.

Source

Thrown at conversions/octal_to_hexadecimal.py:31

    TypeError: Expected a string as input
    >>> octal_to_hex("Av")
    Traceback (most recent call last):
        ...
    ValueError: Not a Valid Octal Number
    >>> octal_to_hex("")
    Traceback (most recent call last):
        ...
    ValueError: Empty string was passed to the function
    """

    if not isinstance(octal, str):
        raise TypeError("Expected a string as input")
    if octal.startswith("0o"):
        octal = octal[2:]
    if octal == "":
        raise ValueError("Empty string was passed to the function")
    if any(char not in "01234567" for char in octal):
        raise ValueError("Not a Valid Octal Number")

    decimal = 0
    for char in octal:
        decimal <<= 3
        decimal |= int(char)

    hex_char = "0123456789ABCDEF"

    revhex = ""
    while decimal:
        revhex += hex_char[decimal & 15]
        decimal >>= 4

    return "0x" + revhex[::-1]


if __name__ == "__main__":
    import doctest

View on GitHub (pinned to f5988cc097)

Solutions

1. Validate the charset before calling: all(c in '01234567' for c in s.removeprefix('0o')).
2. If the input is actually hex, use the hex-to-octal path or hexadecimal_conversion instead.
3. Normalize/clean input (strip whitespace, lowercase, drop '0o') before validation.

Example fix

# before
octal_to_hex('Av')  # ValueError: Not a Valid Octal Number

# after
s = 'Av'.removeprefix('0o')
if not s or any(c not in '01234567' for c in s):
    raise ValueError(f'{s!r} is not octal')
octal_to_hex(s)

OCTAL_DIGITS = set('01234567')
s = octal.removeprefix('0o')
if not s or any(c not in OCTAL_DIGITS for c in s):
    raise ValueError(f'{octal!r} is not a valid octal number')
octal_to_hex(s)

def is_valid_octal(s: str) -> bool:
    s = s.removeprefix('0o')
    return bool(s) and all(c in '01234567' for c in s)

try:
    octal_to_hex(octal)
except ValueError as e:
    if 'Not a Valid Octal Number' in str(e):
        log_invalid_input(octal)
    else:
        raise

When it happens

Trigger: Calling octal_to_hex('Av'), octal_to_hex('8'), octal_to_hex('12 3') (space), or passing a hex string like '1FF' by mistake.

Common situations: Swapping argument order in a bidirectional converter and feeding a hex string where octal is expected; user typos; data pipelines that mix base-8 and base-16 identifiers.

Related errors

• Non-octal value was passed to the function
• 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/b16053a20dfb2bac. Report an issue: GitHub.