how to remove the same words in the paragraph

I need to remove the word if it appears in the paragraph twice. could some give me some clue or some useful function in the python. -- http://mail.python.org/mailman/listinfo/python-list

how to remove the punctuation and no need words from paragraphs

I want to remove all the punctuation and no need words form a string datasets for experiment. I am new to python, please give me some clue and direction to write this code. -- http://mail.python.org/mailman/listinfo/python-list