conversion of string representing HH:MM:SS.sss format into HH:MM:SS.ssssss format in python

I have string which is representing time in HH:MM:SS.sss format ,Now i have to convert this sting into HH:MM开发者_JAVA技巧:SS.ssssss format.Please let me know how to do this?

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Can you not just append "000" on the end?

So "13:23:12.345" => "13:23:12.345000"