TheAlgorithms/Python · error · ValueError

Base16 encoded data is invalid: Data is not uppercase hex or

Error message

Base16 encoded data is invalid:
Data is not uppercase hex or it contains invalid characters.

What it means

Raised by base16_decode() when the input contains characters outside the canonical uppercase hex alphabet '0123456789ABCDEF' (RFC 3548 section 6). The check `set(data) <= set('0123456789ABCDEF')` runs after the even-length check, so lowercase hex ('a'-'f'), whitespace, 'x' prefixes, and punctuation all fail.

Source

Thrown at ciphers/base16.py:54

    ValueError: Base16 encoded data is invalid:
    Data is not uppercase hex or it contains invalid characters.
    >>> base16_decode('This is not base64 encoded data.')
    Traceback (most recent call last):
      ...
    ValueError: Base16 encoded data is invalid:
    Data is not uppercase hex or it contains invalid characters.
    """
    # Check data validity, following RFC3548
    # https://www.ietf.org/rfc/rfc3548.txt
    if (len(data) % 2) != 0:
        raise ValueError(
            """Base16 encoded data is invalid:
Data does not have an even number of hex digits."""
        )
    # Check the character set - the standard base16 alphabet
    # is uppercase according to RFC3548 section 6
    if not set(data) <= set("0123456789ABCDEF"):
        raise ValueError(
            """Base16 encoded data is invalid:
Data is not uppercase hex or it contains invalid characters."""
        )
    # For every two hexadecimal digits (= a byte), turn it into an integer.
    # Then, string the result together into bytes, and return it.
    return bytes(int(data[i] + data[i + 1], 16) for i in range(0, len(data), 2))


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Uppercase the input: base16_decode(data.upper()) once length is even.
2. Strip prefixes/space: data.removeprefix('0x').replace(' ', '').upper().
3. Prefer bytes.fromhex(data) if you actually want case-insensitive lowercase-tolerant decoding.

Example fix

# before
base16_decode('deadbeef')  # ValueError: not uppercase hex

# after
base16_decode('DEADBEEF')  # b'\xde\xad\xbe\xef'

data = data.strip().removeprefix('0x').upper()
if not set(data) <= set('0123456789ABCDEF'):
    raise ValueError(f'invalid hex characters in {data!r}')

def is_uppercase_hex(s: str) -> bool:
    return len(s) % 2 == 0 and set(s) <= set('0123456789ABCDEF')

try:
    base16_decode(data)
except ValueError as e:
    if 'uppercase hex' in str(e):
        base16_decode(data.upper())
    else:
        raise

When it happens

Trigger: Calling base16_decode('this is not base64 encoded data.') as in the doctest, base16_decode('deadbeef') (lowercase), or base16_decode('0xFF') (0x prefix).

Common situations: Feeding bytes.hex() output (which is lowercase) directly to the decoder, strings with a '0x' prefix from hex literals, or whitespace from copy-paste.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Base16 encoded data is invalid: Data does not have an even n
• plain must contain only lowercase letters (a-z)
• plaintext is empty
• key is empty
• ciphertext is empty

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/e87a65e2b5119694. Report an issue: GitHub.