from typing import List


def get_param_docstring(docstring: str) -> str:
    """
    Get docstring of argument part.

    Parameters
    ----------
    docstring : str
        Target docstring string.

    Returns
    -------
    param_docstring : str
        Argument part docstring.
    """
    param_part_started: bool = False
    initial_hyphen_appeared: bool = False
    line_splitted_docstring_list: List[str] = docstring.split('\n')
    param_docstring: str = ''
    pre_line_str: str = ''
    second_hyphen_exists: bool = False
    for line_str in line_splitted_docstring_list:
        if line_str == '    Parameters':
            param_part_started = True
            continue
        is_hyphen_line: bool = '----' in line_str
        if (param_part_started
                and not initial_hyphen_appeared
                and is_hyphen_line):
            initial_hyphen_appeared = True
            continue
        if not initial_hyphen_appeared:
            continue
        if is_hyphen_line:
            second_hyphen_exists = True
            break

        if pre_line_str != '':
            if param_docstring != '':
                param_docstring += '\n'
            param_docstring += pre_line_str
        pre_line_str = line_str

    if not second_hyphen_exists:
        if param_docstring != '':
            param_docstring += '\n'
        param_docstring += pre_line_str
    return param_docstring