---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-12-e95958d05d62> in <cell line: 88>()
     90     fixed_seed = 42
     91     try:
---> 92         result = characters_to_sentences(sample_characters, fixed_seed)
     93         print(result)
     94     except ValueError as e:

<ipython-input-12-e95958d05d62> in characters_to_sentences(characters, seed)
     34         if not sentence_words:
     35             continue
---> 36         sentence = ' '.join(sentence_words)
     37         sentence = sentence.capitalize() + '.'
     38         formatted_sentences.append(sentence)

TypeError: sequence item 0: expected str instance, list found
import random
from typing import List, Any


def characters_to_sentences(characters: List[str], seed: int) -> str:
    """
    Combines a list of characters into sentences using a fixed random seed.

    :param characters: List of single-character strings.
    :param seed: Integer seed for randomization to ensure reproducibility.
    :return: A string consisting of sentences formed from the input characters.
    :raises ValueError: If input is invalid.
    """
    _validate_input(characters, seed)

    rng = random.Random(seed)

    # Shuffle characters to ensure random distribution
    shuffled_chars = characters.copy()
    rng.shuffle(shuffled_chars)

    # Group characters into words
    words = _group_elements(shuffled_chars, rng, min_size=2, max_size=8)

    # Shuffle words to randomize sentence construction
    rng.shuffle(words)

    # Group words into sentences
    sentences = _group_elements(words, rng, min_size=5, max_size=15)

    # Capitalize first word of each sentence and add a period at the end
    formatted_sentences = []
    for sentence_words in sentences:
        if not sentence_words:
            continue
        sentence = ' '.join(sentence_words)
        sentence = sentence.capitalize() + '.'
        formatted_sentences.append(sentence)

    return ' '.join(formatted_sentences)


def _validate_input(characters: List[Any], seed: Any) -> None:
    """
    Validates the input parameters.

    :param characters: The list to validate.
    :param seed: The seed to validate.
    :raises ValueError: If validation fails.
    """
    if not isinstance(characters, list):
        raise ValueError("Characters input must be a list.")

    if not all(isinstance(c, str) and len(c) == 1 for c in characters):
        raise ValueError("All items in characters list must be single-character strings.")

    if not isinstance(seed, int):
        raise ValueError("Seed must be an integer.")

    if not characters:
        raise ValueError("Characters list cannot be empty.")


def _group_elements(elements: List[str], rng: random.Random, min_size: int, max_size: int) -> List[List[str]]:
    """
    Groups elements into sublists based on random sizes.

    :param elements: The list of elements to group.
    :param rng: A random number generator instance.
    :param min_size: Minimum size of each group.
    :param max_size: Maximum size of each group.
    :return: A list of grouped elements.
    """
    groups = []
    index = 0
    total = len(elements)
    while index < total:
        remaining = total - index
        group_size = rng.randint(min_size, max_size)
        group_size = min(group_size, remaining)
        group = elements[index:index + group_size]
        groups.append(group)
        index += group_size
    return groups


# Example Usage
if __name__ == "__main__":
    sample_characters = list("abcdefghijklmnopqrstuvwxyz")
    fixed_seed = 42
    try:
        result = characters_to_sentences(sample_characters, fixed_seed)
        print(result)
    except ValueError as e:
        print(f"Error: {e}")