@classmethod
def fromkeys(cls, iterable, value=None):
    """
        Similar to :meth:`dict.fromkeys`--creates a new `Header` from an
        iterable of keywords and an optional default value.

        This method is not likely to be particularly useful for creating real
        world FITS headers, but it is useful for testing.

        Parameters
        ----------
        iterable
            Any iterable that returns strings representing FITS keywords.

        value : optional
            A default value to assign to each keyword; must be a valid type for
            FITS keywords.

        Returns
        -------
        header
            A new `Header` instance.
        """
    d = cls()
    if not isinstance(value, tuple):
        value = value,
    for key in iterable:
        d.append((key,) + value)
    return d
