concise code (beginner)

[James Stroud]

Karthik Gurusamy wrote:
> On Sep 5, 11:17 am, James Stroud <jstr... at mbi.ucla.edu> wrote:
>> 
>> for i in xrange(number_of_reads):
>>    for dev in devs:
>>      try:
>>        _reader = getattr(dev, 'read%d' % i)
>>        _reader()
>>      except Exception, e:
>>        print e
>>        devs.remove(dev)
> 
> I see in many of the solutions suggested above, the devs sequence/
> iterator is being modified while iterating. I know it is not defined
> for interation over dictionary keys. Are they defined for other
> collections like lists?

Good eye! My code is broke as you have noticed:

py> r = range(5)
py> for i in r:
...   print i
...   if i % 2:
...     r.remove(i)
...
0
1
3


For longer sequences, the algorithm I've used in these cases in the past 
goes something like this:

py> r = range(10, 17)
py> print r
[10, 11, 12, 13, 14, 15, 16]
py>
py> i = 0
py> while i < len(r):
...   j = r[i]
...   print j
...   if j % 2:
...     r.remove(j)
...   else:
...     i += 1
...
10
11
12
13
14
15
16
py> print r
[10, 12, 14, 16]


Which would change my problematic code above to:


for i in xrange(number_of_reads):
   j = 0
   while j < len(devs):
     try:
       _reader = getattr(devs[j], 'read%d' % i)
       _reader()
       j += 1
     except Exception, e:
       print e
       devs.remove(dev)

Another way is to make a copy of devs, if devs is short, which makes my 
problematic code into a matter of a "typo"--maybe I can make this claim 
to save some face?

for i in xrange(number_of_reads):
   for dev in devs[:]:
     try:
       _reader = getattr(dev, 'read%d' % i)
       _reader()
     except Exception, e:
       print e
       devs.remove(dev)

James

-- 
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/