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There are two versions 2.7 and 3.2 at present. There are some differences between them in the way that the programs are written
for example
print "Hello Pi" version 2.7
print ("Hello Pi") version 3.2
Choosing version 2.7 links with most of the books and other texts on Python
I will cover both versions here as the Raspbian "Wheezy" uses Python 3.2