CODEWITHSUNDEEP
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dotancohen
dotancohen

Reputation: 31491

Remove the object being iterated over from list

Consider:

fooList = [1, 2, 3, 4] # Ints for example only, in real application using objects

for foo in fooList:
    if fooChecker(foo):
        remove_this_foo_from_list

How is the specific foo to be removed from the list? Note that I'm using ints for example only, in the real application there is a list of arbitrary objects.

Thanks.

Upvotes: 1

Views: 147

Answers (3)

Ashwini Chaudhary
Ashwini Chaudhary

Reputation: 251021

Iterate over a shallow copy of the list.

As you can't modify a list while iterating over so you need to iterate over a shallow copy of the list.

fooList = [1, 2, 3, 4] 

for foo in fooList[:]: #equivalent to list(fooList), but much faster
    if fooChecker(foo):
        fooList.remove(foo)

Upvotes: 8

Gareth Latty
Gareth Latty

Reputation: 89027

Generally, you just don't want to do this. Instead, construct a new list instead. Most of the time, this is done with a list comprehension:

fooListFiltered = [foo for foo in fooList if not fooChecker(foo)]

Alternatively, a generator expression (my video linked above covers generator expressions as well as list comprehensions) or filter() (note that in 2.x, filter() is not lazy - use a generator expression or itertools.ifilter() instead) might be more appropriate (for example, a large file that is too big to be read into memory wouldn't work this way, but would with a generator expression).

If you need to actually modify the list (rare, but can be the case on occasion), then you can assign back:

fooList[:] = fooListFiltered

Upvotes: 8

Paul
Paul

Reputation: 21985

Use filter:

newList = list(filter(fooChecker, fooList))

or

newItems = filter(fooChecker, fooList))

for item in newItems:
    print item # or print(item) for python 3.x

http://docs.python.org/2/library/functions.html#filter

Upvotes: -1

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