def get_cgi_parameter_float(form: cgi.FieldStorage,
                            key: str) -> Optional[float]:
    """
    Extracts a float parameter from a CGI form, or None if the key is
    absent or the string value is not convertible to ``float``.
    """
    return get_float_or_none(get_cgi_parameter_str(form, key))
Extracts a float parameter from a CGI form, or None if the key is
    absent or the string value is not convertible to ``float``.