Better to add item to a set, or convert final list to a set?

Question

I have some data that looks something like this:

ID1 ID2 ID3  
ID1 ID4 ID5  
ID3 ID5 ID7 ID6  
...  
...  

where each row is a group.

M

Answer 1

i agree with the previous analysis that option B is best, but a micro benchmark is often illuminating in these situations:

import time

class Timer(object):
  def __init__(self, desc):
    self.desc = desc
  def __enter__(self):
    self.start = time.time()
  def __exit__(self, type, value, traceback):
    self.finish = time.time()
    print self.desc, 'took', self.finish - self.start

data = list(range(4000000))

with Timer('option 2'):
  myset = set()
  for x in data: myset.add(x)

with Timer('option 3'):
  mylist = list()
  for x in data: mylist.append(x)
  myset = set(mylist)

the results were surprising to me:

$ python test.py 
option 2 took 0.652163028717
option 3 took 0.748883008957

i would have expected at least a 2x speed difference.