Python things which are neither True nor False

I just found this :

a = (None,)
print (a is True)
print (a is False)
print (a == True)
print (a == False)
print (a == None)
print (a is None)
if a : print "hello"
if not a : print "goodbye"

which produces :

False
False
False
False
False
False
hello

So a neither is, nor equals True nor False, but acts as True in an if statement.

Why?

Update :

actually, I've just realized that this isn't as obscure as I thought. I get the same result for a=2, as well (though not for a=0 or a=1, which are considered equal to False and True respectively)