Confused over Lists

Paul Brian paul1brian at yahoo.com
Fri Aug 2 15:56:47 CEST 2002


Dear all,

If I have a list of items, and wish to test each item, and remove those
items that meet a certain criteria, I assumed I could use list.remove()

however I came across the following problem:

imagine a list of numbers, [1,1,2,3,4,5] and I wish to remove all the 1's.

the following I thought should work :-

demoList = [1, 1, 2, 3, 4, 5]
for num in demoList:
    if num == 1:
        demoList.remove(num)
print demoList

but I get
>>> [1, 2, 3, 4, 5]


There appears to be a magic counter that keeps track of what index it has
already iteratered over in the list.
When the first "1" is encountered (index 0) it removes it, and shifts the
next "1" to index 0.
But the magic counter thinks it has already visited index 0 and so "blips"
over the second 1, thus not removing that "1" from the list.

Now this does make sense, and I can get round it using seperate lists as
stores, but 2 questions

1) Am I missing something really obvious on how to handle this the way I
think it *should* work (NB absolutley no PEP orientated issues here - no
desire to try and say we should change behaviour of lists cos i dont get it)

2) How do I get access to that magic counter. It would be very useful in all
sorts of ways.

Thank you :-)



------------------------------
Paul Brian
(07899) 877 295
paul1brian at yahoo.com







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