CODEWITHSUNDEEP
python
user1427661
user1427661

Reputation: 11774

Remove Element From List Without Index

So I'm iterating over items in a list in this way:

for virus in viruses:
    do stuff
    remove virus

If I had the index, I could just do del virus[i], and I could obviously tweak the code to do something like for index in range(0, len(viruses)), but that starts to make the code ugly pretty quickly for the other things I want to do within the for loop. Is there anyway I can just remove based on the name of the virus I am currently iterating over?

Upvotes: 4

Views: 12590

Answers (4)

Merbs
Merbs

Reputation: 387

Although one of your options is to use remove(), that may return an error. Another option is to treat viruses (which is assumed to be a list) as a stack (or a queue)

for _ in xrange(len(viruses)):
    virus = viruses.pop()
    # do stuff with virus

If viruses is instead a dictionary (and virus the key), then the key is all you need to delete it:

import copy
for virus in copy.copy(viruses):
    # do stuff with virus
    del viruses[virus]

See http://docs.python.org/tutorial/datastructures.html for more information

Upvotes: 0

arshajii
arshajii

Reputation: 129507

How about this:

for virus in viruses[:]:
    # do stuff
    viruses.remove(virus)  # remove "virus" from the original list

viruses[:] creates a copy of our viruses list. As a note, you can also use list(oldlist) to copy lists (I find this a little more readable, but either will work). You can read more about lists in python here.

Upvotes: 10

Andrew Clark
Andrew Clark

Reputation: 208465

To remove an item by its value just use list.remove():

Removing elements from a list while you are iterating over it can cause some unexpected problems, so make sure you are iterating over a copy:

for virus in viruses[:]:
    # do stuff
    viruses.remove(virus)

Upvotes: 5

Ashwini Chaudhary
Ashwini Chaudhary

Reputation: 250931

lists have a method remove(), using which you can remove an element by value,

and if you're modifying a list as well as iterating over it then you should use reversed(), otherwise the iteration will miss some elements:

for virus in reversed(viruses):
    viruses.remove(virus)

a simple example:

In [203]: lis=range(0,10)

In [206]: for x in reversed(lis):
   .....:     if x%2==0:                #remove even numbers
   .....:         lis.remove(x)
   .....:         
   .....:         

In [207]: lis
Out[207]: [1, 3, 5, 7, 9]

or use a shallow copy:

In [212]: lis=range(10)

In [213]: for x in lis[:]:
    if x%2==0:
        lis.remove(x)
   .....:         
   .....:         

In [216]: lis
Out[216]: [1, 3, 5, 7, 9]

Upvotes: 1

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