'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.'

@classmethod
def fromkeys(cls, iterable, value=None):

    d = cls()
    if (not isinstance(value, tuple)):
        value = (value,)
    for key in iterable:
        d.append(((key,) + value))
    return d
