def common_completion_suffix_validator(df: pd.DataFrame) -> Remediation:
    """
    This validator will suggest to add a common suffix to the completion if one doesn't already exist in case of classification or conditional generation.
    """
    error_msg = None
    immediate_msg = None
    optional_msg = None
    optional_fn = None  # type: ignore

    ft_type = infer_task_type(df)
    if ft_type == "open-ended generation" or ft_type == "classification":
        return Remediation(name="common_suffix")

    common_suffix = get_common_xfix(df.completion, xfix="suffix")
    if (df.completion == common_suffix).all():
        error_msg = f"All completions are identical: `{common_suffix}`\nEnsure completions are different, otherwise the model will just repeat `{common_suffix}`"
        return Remediation(name="common_suffix", error_msg=error_msg)

    # Find a suffix which is not contained within the completion otherwise
    suggested_suffix = " [END]"
    suffix_options = [
        "\n",
        ".",
        " END",
        "***",
        "+++",
        "&&&",
        "$$$",
        "@@@",
        "%%%",
    ]
    for suffix_option in suffix_options:
        if df.completion.str.contains(suffix_option, regex=False).any():
            continue
        suggested_suffix = suffix_option
        break
    display_suggested_suffix = suggested_suffix.replace("\n", "\\n")

    def add_suffix(x: Any, suffix: Any) -> Any:
        x["completion"] += suffix
        return x

    if common_suffix != "":
        common_suffix_new_line_handled = common_suffix.replace("\n", "\\n")
        immediate_msg = f"\n- All completions end with suffix `{common_suffix_new_line_handled}`"
        if len(common_suffix) > 10:
            immediate_msg += f". This suffix seems very long. Consider replacing with a shorter suffix, such as `{display_suggested_suffix}`"
        if df.completion.str[: -len(common_suffix)].str.contains(common_suffix, regex=False).any():
            immediate_msg += f"\n  WARNING: Some of your completions contain the suffix `{common_suffix}` more than once. We suggest that you review your completions and add a unique ending"

    else:
        immediate_msg = "\n- Your data does not contain a common ending at the end of your completions. Having a common ending string appended to the end of the completion makes it clearer to the fine-tuned model where the completion should end. See https://platform.openai.com/docs/guides/fine-tuning/preparing-your-dataset for more detail and examples."

    if common_suffix == "":
        optional_msg = f"Add a suffix ending `{display_suggested_suffix}` to all completions"

        def optional_fn(x: Any) -> Any:
            return add_suffix(x, suggested_suffix)

    return Remediation(
        name="common_completion_suffix",
        immediate_msg=immediate_msg,
        optional_msg=optional_msg,
        optional_fn=optional_fn,
        error_msg=error_msg,
    )

    This validator will suggest to add a common suffix to the completion if one doesn't already exist in case of classification or conditional generation.
    
src/openai/lib/_validators.py