def parse_arg(x):
    """
    Parse a string argument and attempt to turn numbers into actual
    number types.
    
    Parameters
    ----------
    x : str
        A string arg.
    
    Returns
    -------
    str, float, or int
        x type converted.
    """
    
    if x.replace('.', '').isdigit():
        if x.isdigit():
            x = int(x)
        else:
            x = float(x)
                
    return x