TheAlgorithms/Python · error · ValueError

Invalid IPv4 octet {octet}

Error message

Invalid IPv4 octet {octet}

What it means

Raised by ipv4_to_decimal(ipv4_address) in conversions/ipv4_conversion.py:35 when an octet parses as an integer but falls outside 0..255. The function checks each of the four parts after the count check, so a well-formed dotted quad with an out-of-range value ('10.0.0.256', '300.1.1.1', '-1.0.0.0' style negatives) raises ValueError(f"Invalid IPv4 octet {octet}") naming the offending octet.

Source

Thrown at conversions/ipv4_conversion.py:35

    167772415
    >>> ipv4_to_decimal("10.0.255")
    Traceback (most recent call last):
        ...
    ValueError: Invalid IPv4 address format
    >>> ipv4_to_decimal("10.0.0.256")
    Traceback (most recent call last):
        ...
    ValueError: Invalid IPv4 octet 256
    """

    octets = [int(octet) for octet in ipv4_address.split(".")]
    if len(octets) != 4:
        raise ValueError("Invalid IPv4 address format")

    decimal_ipv4 = 0
    for octet in octets:
        if not 0 <= octet <= 255:
            raise ValueError(f"Invalid IPv4 octet {octet}")  # noqa: EM102
        decimal_ipv4 = (decimal_ipv4 << 8) + int(octet)

    return decimal_ipv4


def alt_ipv4_to_decimal(ipv4_address: str) -> int:
    """
    >>> alt_ipv4_to_decimal("192.168.0.1")
    3232235521
    >>> alt_ipv4_to_decimal("10.0.0.255")
    167772415
    """
    return int("0x" + "".join(f"{int(i):02x}" for i in ipv4_address.split(".")), 16)


def decimal_to_ipv4(decimal_ipv4: int) -> str:
    """
    Convert a decimal representation of an IP address to its IPv4 format.

View on GitHub (pinned to f5988cc097)

Solutions

1. Clamp or wrap overflowing octets: carry into the previous octet when the last exceeds 255
2. Validate up front with ipaddress.IPv4Address(addr) and catch ValueError
3. If generating from integers, ensure the source int is already in 0..4294967295 and use decimal_to_ipv4 instead

Example fix

# before
ip = f'10.0.0.{250 + i}'  # i > 5 -> ValueError
ipv4_to_decimal(ip)

# after
import ipaddress
ip = str(ipaddress.IPv4Address(ipaddress.IPv4Address('10.0.0.250') + i))
ipv4_to_decimal(ip)

parts = ipv4_address.split('.')
if len(parts) != 4 or not all(p.isdigit() and 0 <= int(p) <= 255 for p in parts):
    raise ValueError(f'invalid IPv4: {ipv4_address!r}')

When it happens

Trigger: ipv4_to_decimal('10.0.0.256'), ipv4_to_decimal('999.999.999.999'), or octets computed arithmetically (base + offset) that overflow 255.

Common situations: Incrementing the last octet past 255 when generating IPs in a loop; user-typed addresses with typos; values from counters that wrap into the next /24 without carries.

Related errors

• Invalid decimal IPv4 address
• Invalid IPv4 address format
• base must be >= 2
• base must be <= 36
• No input value was provided

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/65c2c1ae455ac8e8. Report an issue: GitHub.