[AstroPy] DATAMD5 calculation

[Erik Bray]

On 05/24/2011 06:08 PM, Erik Bray wrote:
> At any rate, in the meantime you can use hashlib to generate a checksum
> on hdu.data--no need to use any internal attributes:
>
> import hashlib
> md5sum = hashlib.md5()
> md5sum.update(hdu.data.tostring())

I should add, the tostring() here was a typo--I don't know why I thought 
to insert that.  just md5sum.update(hdu.data) is sufficient.  Calling 
tostring() is a bad idea, since it actually causes the array to be copied.

> hdu.header['DATAMD5'] = md5sum.hexdigest()
>
> My version of hashlib seems to know how to efficiently handle objects
> that implement the buffer interface (i.e. numpy arrays), so this should
> be pretty fast.
>
> Erik
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