how to delete hyphen in filename and add something to the name ? python
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i have a folder with a lot of files like that:

    2012-05-09.txt
    2012-05-10.txt
    2012-05-11.txt
    etc. 

now i wanna delete the hyphen and add " _PHOTOS_LOG " that it looks in the end like this:

    20120509_PHOTOS_LOG.txt
    20120510_PHOTOS_LOG.txt
    20120511_PHOTOS_LOG.txt
    etc.

How to do ? 