list comprehension syntax..?

[Gregory Guthrie]

Very helpful, thanks!!

So I see that it parses as:


  m='1'
  a="asdf"
  b="1234"
  print [((m in a) or b) for m in '%d'%1234 ]


I get it.
Thanks,
Greg


"Duncan Booth" <duncan.booth at invalid.invalid> wrote in message 
news:Xns9812BD37F7717duncanbooth at 127.0.0.1...
> Gregory Guthrie wrote:
>
>> Sorry for a simple question- but I don't understand how to parse this
>> use of a list comprehension.
>>
>> The "or" clauses are odd to me.
>>
>> It also seems like it is being overly clever (?) in using a lc
>> expression as a for loop to drive the recursion.
>
> You are spot on there. It is a list comprehension, but the resulting list
> is just thrown away, so using a list comprehension is a complete waste of
> time serving only to confuse the issue. Presumably it saved the author a
> character or two.
>
> [ exp for var in seq ]
>
> when the result isn't used can be rewritten as:
>
> for var in seq:
>   exp
>
> and:
>
>   exp1 or exp2
>
> when the result is thrown away is just:
>
>   if not exp1:
>       exp2
>
>
> So:
>
> [ m in [(i-j)%9*(i/9^j/9)*(i/27^j/27|i%9/3^j%9/3)
>          or board[j] for j in range(81) ]
>     or solve(board[:i]+m+board[i+1:]) for m in'%d'%5**18 ]
>
> is equivalent to:
>
> inner = [(i-j)%9*(i/9^j/9)*(i/27^j/27|i%9/3^j%9/3) or board[j] for j in
> range(81) ]
> for m in '3814697265625':
>    if m not in inner:
>         solve(board[:i]+m+board[i+1:])
>
> (That inner list comprehension doesn't depend on m, so it doesn't need to
> be reevaluated each time round the loop except, again, to save a few
> characters.)
>
> The '%d'%5**18 looks to be a silly way to iterate through all possible
> digits for m even though it does some of them twice while saving one
> character over writing range(1,10).
>
> The strange expression I called 'inner' is a list containing the string
> value board[j] if j is in the same row, column or block as i, or an 
> integer
> for any other cells. So 'm not in inner' is true only if the value for m 
> is
> not already used in that row column or block and is therefore a possible
> candidate for that location in the board. 



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