Re: [Tutor] Loop blocks

[cs]

On 10Jun2016 22:41, Jignesh Sutar  wrote:

Is there a better way to code the below than to specify blocks as I have.
Ideally I'd like to specify blocks simply as *blocks=(12,20,35)*

blocks=[(1,12), (13,20), (25,35)]
for i,j in enumerate(blocks):
   for x in xrange(blocks[i][0],blocks[i][1]+1):
   print i+1, x


For one thing I don't see you use "j" anywhere. Why not this:

 for i, block in enumerate(blocks):
 for x in xrange(block[0], block[1]+1):
 print i+1, x

enumerate() returns a counter _and_ the element from what it iterates over.

You can also start enumerate from 1 instead of zero; since the code above no 
longer used "i" as an index into "blocks" (because you get handed the block by 
enumerate) you could count from one to avoid computing "i+1".


Finally, your question: Ideally I'd like to specify blocks simply as:

 blocks=(12,20,35)

why not just do that? I don't see you using the leading number, and if it is 
meant to be the "i+1" in your code, you get that from enumerate already.


Cheers,
Cameron Simpson 
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Re: [Tutor] Fwd: Re: Loop in pre-defined blocks

[Peter Otten]

Alan Gauld via Tutor wrote:

> Forwarding to tutor list. Always use Reply All when responding to list
> mail.
> 
>> Sorry, to be a little bit more descriptive. I'd like to loop from 1 to 35
>> but within this loop there are divisions which I need to prefix that
>> particular division number.
> 
>> My output would look like this:

> 1 1
> 1 2
> 1 3
> 1 4
> 1 5
> 1 6
> 1 7
> 1 8
> 1 9
> 1 10
> 1 11
> 1 12
> 2 13
> 2 14
> 2 15
> 2 16
> 2 17
> 2 18
> 2 19
> 2 20
> 3 25
> 3 26
> 3 27
> 3 28
> 3 29
> 3 30
> 3 31
> 3 32
> 3 33
> 3 34
> 3 35

> 
> You can't specify the blocks as just (12,20,.35) since you are using
> non-contiguous blocks - you have a gap between 20 and 25.
> 
> So your definition needs to be (1,12),(13,20),(25,35) to specify
> the missing rows. But you can arguably simplify the code a little:
> 
> blocks = ((1,13),(13,21),(25,36))
> for prefix, block in enumerate(blocks):
>  for n in range(*block):
>   print prefix+1, n
> 
> its very similar to your code but using tuple expansion in range()
> cleans it up a little bit and the names hopefully make the intent
> clearer.

As Alan says, you need to specify the gaps. A simple if hackish way is to 
use negative numbers:

def expand(ends):
start = 1
for end in ends:
if end < 0:
start = -end
else:
end += 1
yield (start, end)
start = end

blocks = [12, 20, -25, 35]
for index, span in enumerate(expand(blocks), 1):
for x in xrange(*span):
print index, x


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