Append to python List

[RAHUL RAJ]

Then what about this code part?

[(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]

and the following code part:

for x in [1,2,3]:
  for y in [3,1,4]:
    if x != y:
      combs.append((x, y))


On Thursday, May 9, 2013 12:24:24 PM UTC+5:30, Gary Herron wrote:
> On 05/08/2013 11:36 PM, RAHUL RAJ wrote:
> 
> > 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]
> 
> This statement is not doing what you expect.  It is not building a list 
> 
> in the variable named output, it is building a list (anonymously) then 
> 
> binding it to the variable output once it's built.  Therefore output is 
> 
> [] for the whole list building operation.
> 
> 
> 
> The later operation works, because your *are* building the list in place 
> 
> as you go.
> 
> 
> 
> >
> 
> > 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.
> 
> >
> 
> >
> 
> >
> 
> >
> 
> > But if I do like this:
> 
> >
> 
> > sample2 = [x+y for x in range(1,10) for y in range(1,10) if x!=y]
> 
> > output=[]
> 
> > for x in sample2:
> 
> >    if x not in output:
> 
> >       output.append(x)
> 
> >
> 
> >
> 
> > the value of 'output' I get like this:
> 
> > 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
> 
> >
> 
> > I know that both the programs have the same functionality, but why do I have different outputs?
> 
> >
> 
> > Please help!