I am having trouble with a list of sets and I think it is because I initialized it wrong, is this a valid way to initialize and add to a list of 5000 sets?
sets = [set()]*5000
i = 0
for each in f:
line = each.split()
if (some statement):
i = line[1]
else:
sets[i].add(line[0])
any advice would be much appreciated
You are storing a copy of reference to a single set in each of your list indices. So, modifying one will change the others too.
To create a list of multiple sets, you can use list comprehension:
sets = [set() for _ in xrange(5000)]
This works:
>>> lotsosets=[set() for i in range(5)]
>>> lotsosets
[set([]), set([]), set([]), set([]), set([])]
>>> lotsosets[0].add('see me?')
>>> lotsosets
[set(['see me?']), set([]), set([]), set([]), set([])]
>>> lotsosets[1].add('imma here too')
>>> lotsosets
[set(['see me?']), set(['imma here too']), set([]), set([]), set([])]
You should only use the form [x]*5000 if x is something immutable:
>>> li=[None]*5
>>> li
[None, None, None, None, None]
>>> li[0]=0
>>> li
[0, None, None, None, None]
>>> li[1]=1
>>> li
[0, 1, None, None, None]
Or if having multiple references to a single item, like an iterator, produces desired behavior:
>>> [iter('abc')]*3
[<iterator object at 0x100498410>,
<iterator object at 0x100498410>,
<iterator object at 0x100498410>] # 3 references to the SAME object
Note the repeated reference to the same iterator which then produces a desired behavior with zip:
>>> zip(*[iter('abcdef')]*3)
[('a', 'b', 'c'), ('d', 'e', 'f')]
Or a subset of a longer iterator:
>>> [next(x) for x in [iter('abcdef')]*3]
['a', 'b', 'c']
Whereas something like [list()]*5 is probably not producing what is intended:
>>> li=[list()]*5
>>> li
[[], [], [], [], []]
>>> li[0].append('whoa')
>>> li
[['whoa'], ['whoa'], ['whoa'], ['whoa'], ['whoa']]
[set() for _ in xrange(5000)]for set in sets:statement.for each in f... what'sf? An open file?