def input_to_int(value):
    """
    Checks that user input is an integer.

    Parameters
    ----------
    n : user input to check

    Returns
    -------
    integer : n cast to an integer

    Raises
    ------
    ValueError : if n is not an integer
    """
    if str(value).isdigit():
        return int(value)
    else:
        raise ValueError('Expecting integer. Got: "{0}" ({1})'
                         .format(value, type(value)))