from typing import List


def prepare_corpus(docs: List[str]) -> List[str]:
    """Cleans and prepares a list of documents for sentiment analysis

    Parameters
    ----------
    docs: List[str]
        A list of documents to prepare for sentiment analysis

    Returns
    -------
    List[str]
        List of cleaned and prepared docs
    """
    docs = [doc.lower().strip() for doc in docs]

    def clean_text(doc):
        out = []
        for c in doc:
            if c.isalpha() or c.isspace():
                out.append(c)
        return "".join(out)

    docs = [clean_text(doc) for doc in docs]
    return docs