TheAlgorithms/Python · error · ValueError

the words should be a list of non-empty strings

Error message

the words should be a list of non-empty strings

What it means

Raised by word_break() when words is not a list or any element is not a non-empty string. The dictionary is inserted into a trie keyed by individual characters, so empty strings would create degenerate nodes and non-str elements would break char iteration. Both wrong-container and wrong-element cases produce this single message.

Source

Thrown at dynamic_programming/word_break.py:64

    ValueError: the string should be not empty string
    >>> word_break('abc', [123])
    Traceback (most recent call last):
        ...
    ValueError: the words should be a list of non-empty strings
    >>> word_break('abc', [''])
    Traceback (most recent call last):
        ...
    ValueError: the words should be a list of non-empty strings
    """

    # Validation
    if not isinstance(string, str) or len(string) == 0:
        raise ValueError("the string should be not empty string")

    if not isinstance(words, list) or not all(
        isinstance(item, str) and len(item) > 0 for item in words
    ):
        raise ValueError("the words should be a list of non-empty strings")

    # Build trie
    trie: dict[str, Any] = {}
    word_keeper_key = "WORD_KEEPER"

    for word in words:
        trie_node = trie
        for c in word:
            if c not in trie_node:
                trie_node[c] = {}

            trie_node = trie_node[c]

        trie_node[word_keeper_key] = True

    len_string = len(string)

    # Dynamic programming method

View on GitHub (pinned to f5988cc097)

Solutions

1. Normalize to a list of non-empty strings: words = [w for w in words if isinstance(w, str) and w].
2. Wrap sets/tuples: word_break(s, list(words)) after filtering empties.
3. Sanitize file-loaded wordlists by stripping and dropping blank lines.

Example fix

# before
word_break('abc', {'a', 'b', ''})  # ValueError (set + empty string)

# after
word_break('abc', [w for w in ['a', 'b', ''] if w])

def valid_words(words: object) -> bool:
    return isinstance(words, list) and all(
        isinstance(w, str) and len(w) > 0 for w in words
    )

def word_list(words: object) -> TypeGuard[list[str]]:
    return isinstance(words, list) and all(
        isinstance(w, str) and w for w in words
    )

When it happens

Trigger: Calling word_break('abc', ['']) or word_break('abc', [123]) or word_break('abc', 'abc') (a bare string is not a list); a tuple of words also fails since isinstance(words, list) is checked strictly.

Common situations: Deduplicating words into a set or tuple and passing it directly; loading a wordlist where blank lines become '' after .strip(); mixed-type lists from untyped JSON input.

Related errors

• the string should be not empty string
• Limit for the Catalan sequence must be ≥ 0
• Negative arguments are not supported
• iterations must be defined as integers
• starting number must be and integer

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/dd8dc2811597cbaa. Report an issue: GitHub.