How to print each letter in a string only once

How to print each letter in a string only once

References

Reference NO 1

http://stackoverflow.com/questions/15191704/how-to-print-each-letter-in-a-string-only-once

Reference NO 2

http://stackoverflow.com/questions/14092682/how-do-i-check-if-a-string-contains-the-same-letter-more-than-once

Reference NO 3

http://processing.org/tutorials/text/

Reference NO 4

http://en.wikibooks.org/wiki/Python_Programming/Strings

Reference NO 5

http://www.cs.ucf.edu/~dmarino/ucf/juniorknights/python1/Python-Cht4.pdf

Reference NO 6

http://www.openbookproject.net/thinkcs/python/english2e/ch07.html

Reference NO 7

http://www.pythonforbeginners.com/strings/

Reference NO 8

http://web.mit.edu/gnu/doc/html/gawk_6.html