Re: pattern matching with multiple lists

2010-07-16 Thread Tim Chase 

On 07/16/2010 02:20 PM, Chad Kellerman wrote:

Greetings,
  I have some code that I wrote and know there is a better way to
write it.  I  wonder if anyone could point me in the right direction
on making this 'cleaner'.

  I have two lists:   liveHostList = [ app11, app12, web11, web12, host11 ]
 stageHostList  = [  web21,
web22, host21, app21, app22 ]

  I need to pair the elements in the list such that:
 app11  pairs with app21
 app12 pairs with app22
 web11 pairs with web21
 web12 pairs with web22
 host11pairs with host21


While I like MRAB's solution even better than mine[1], you can 
also use:


  liveHostList = ["app11", "app12", "web11", "web12", "host11"]
  stageHostList = ["web21", "web22", "host21", "app21", "app22"]

  def bits(s):
return (s[:-2],s[-1])

  for live, stage in zip(
  sorted(liveHostList, key=bits),
  sorted(stageHostList, key=bits),
  ):
print "Match: ", live, stage

-tkc


[1] His solution is O(N), making one pass through each list, with 
O(1) lookups into the created dict during the 2nd loop, while 
mine is likely overwhelmed by the cost of the sorts...usually O(N 
log N) for most reasonable sorts.  However, this doesn't likely 
matter much until your list-sizes are fairly large.





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Re: pattern matching with multiple lists

2010-07-16 Thread MRAB 

Chad Kellerman wrote:

Greetings,
 I have some code that I wrote and know there is a better way to
write it.  I  wonder if anyone could point me in the right direction
on making this 'cleaner'.

 I have two lists:   liveHostList = [ app11, app12, web11, web12, host11 ]
stageHostList  = [  web21,
web22, host21, app21, app22 ]

 I need to pair the elements in the list such that:
app11  pairs with app21
app12 pairs with app22
web11 pairs with web21
web12 pairs with web22
host11pairs with host21

each time I get the list I don't know the order, and the lists
will grow over time.  (hosts will be added in pairs.  app13 to
liveHostList and app23 to stageHostList, etc)


Anyways this is what I have.  I think it can be written better with
map, but not sure.  Any help would be appreciated.

import re
for liveHost in liveHostlist:

nameList = list(liveHost)
clone= nameList[-1]
di   = nameList[-2]
generic  = liveHost[:-2]

for stageHost in stageHostList:
if re.match( generic + '.' + clone, stageHost ):
print "Got a pair: " + stageHost + liveHost

Thanks again for any suggestions,
Chad


So you recognise a pair by them having the same 'key', which is:

name[ : -2] + name[-1 : ]


Therefore you can put one of the lists into a dict and look up the name
by its key:

liveHostDict = dict((liveHost[ : -2] + liveHost[-1 : ], liveHost) 
for liveHost in liveHostList)


for stageHost in stageHostList:
key = stageHost[ : -2] + stageHost[-1 : ]
liveHost = liveHostDict[key]
print "Got a pair: %s %s" % (stageHost, liveHost)

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