TheAlgorithms/Python · error · ValueError

The parameter bwt_string must not be empty.

Error message

The parameter bwt_string must not be empty.

What it means

Raised by reverse_bwt() in data_compression/burrows_wheeler.py when bwt_string is a str but empty. The inverse BWT needs at least one character to reconstruct rotations, so empty input is rejected right after the type check.

Source

Thrown at data_compression/burrows_wheeler.py:142

    of cast to int.
    >>> reverse_bwt("mnpbnnaaaaaa", -1)
    Traceback (most recent call last):
        ...
    ValueError: The parameter idx_original_string must not be lower than 0.
    >>> reverse_bwt("mnpbnnaaaaaa", 12) # doctest: +NORMALIZE_WHITESPACE
    Traceback (most recent call last):
        ...
    ValueError: The parameter idx_original_string must be lower than
    len(bwt_string).
    >>> reverse_bwt("mnpbnnaaaaaa", 11.0)
    'panamabanana'
    >>> reverse_bwt("mnpbnnaaaaaa", 11.4)
    'panamabanana'
    """
    if not isinstance(bwt_string, str):
        raise TypeError("The parameter bwt_string type must be str.")
    if not bwt_string:
        raise ValueError("The parameter bwt_string must not be empty.")
    try:
        idx_original_string = int(idx_original_string)
    except ValueError:
        raise TypeError(
            "The parameter idx_original_string type must be int or passive"
            " of cast to int."
        )
    if idx_original_string < 0:
        raise ValueError("The parameter idx_original_string must not be lower than 0.")
    if idx_original_string >= len(bwt_string):
        raise ValueError(
            "The parameter idx_original_string must be lower than len(bwt_string)."
        )

    ordered_rotations = [""] * len(bwt_string)
    for _ in range(len(bwt_string)):
        for i in range(len(bwt_string)):
            ordered_rotations[i] = bwt_string[i] + ordered_rotations[i]

View on GitHub (pinned to f5988cc097)

Solutions

1. Check the payload is non-empty before inverting: if bwt_str: reverse_bwt(bwt_str, idx).
2. Investigate why the BWT string is empty — usually upstream data loss or truncation, since bwt_transform() never returns an empty bwt_string for valid input.
3. Treat empty input as a data-integrity error in your pipeline rather than silently skipping.

Example fix

# before
plain = reverse_bwt(bwt_str, idx)  # bwt_str == ''

# after
if not bwt_str:
    raise ValueError('corrupt payload: empty BWT string')
plain = reverse_bwt(bwt_str, idx)

if not bwt_string:
    raise ValueError('corrupt payload: empty BWT string')
plain = reverse_bwt(bwt_string, idx)

try:
    plain = reverse_bwt(bwt_string, idx)
except ValueError:
    plain = ''  # treat as empty original

When it happens

Trigger: Calling reverse_bwt('', 0), or passing an empty string after slicing/trimming a payload, e.g. reverse_bwt(data.split('\x00')[0], idx) when the split yields ''.

Common situations: Decoding a corrupted or truncated compressed payload, handling an empty file/stream chunk, or a pipeline bug that passes an empty placeholder instead of the real BWT output.

Related errors

• The parameter s must not be empty.
• The parameter idx_original_string must not be lower than 0.
• We need some text to work with.
• The parameter s type must be str.
• The parameter bwt_string type must be str.

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/f9106e4331489b34. Report an issue: GitHub.