Append to python List

[Jussi Piitulainen]

RAHUL RAJ writes:

> Checkout the following code:
> 
> sample2 = [x+y for x in range(1,10) for y in range(1,10) if x!=y]   
> output=[]
> output=[x for x in sample2 if x not in output]
> 
> the output I get is
> 3 4 5 6 7 8 9 10 3 5 6 7 8 9 10 11 4 5 7 8 9 10 11 12 5 6 7 9 10 11
> 12 13 6 7 8 9 11 12 13 14 7 8 9 10 11 13 14 15 8 9 10 11 12 13 15 16
> 9 10 11 12 13 14 15 17 10 11 12 13 14 15 16 17
> 
> which contains duplicate values.

The second comprehension, [x for x in sample2 if x not in output], in
the context, is equivalent to [x for x in sample2 if x not in []]. It
does not refer to an incomplete version of the list that gets assigned
to the variable after it's done.