def _destringize_numbers(header):
    """Convert string values in `header` that work as numbers back into
    ints and floats.
    """
    with_numbers = {}
    for key, val in header.items():
        try:
            val = int(val)
        except:
            try:
                val = float(val)
            except:
                pass
        with_numbers[key] = val
    return with_numbers