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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def path_exists_or_creatable_portable(pathname: str) -> bool: """OS-portable check for whether current path exists or is creatable. This function is guaranteed to _never_ raise exceptions. Returns ------ `True` if the passed pathname is a valid pathname on the current OS _and_ either currently exists or is hypothetically creatable in a cross-platform manner optimized for POSIX-unfriendly filesystems; `False` otherwise. """

    try:
        # To prevent "os" module calls from raising undesirable exceptions on
        # invalid pathnames, is_pathname_valid() is explicitly called first.
        return is_pathname_valid(pathname) and (
            os.path.exists(pathname) or is_path_sibling_creatable(pathname))
    # Report failure on non-fatal filesystem complaints (e.g., connection
    # timeouts, permissions issues) implying this path to be inaccessible. All
    # other exceptions are unrelated fatal issues and should not be caught
    # here.
    except OSError:
        return False