CODEWITHSUNDEEP
pythonlist
Bit Bucket
Bit Bucket

Reputation: 952

Remove String From List

I have a list of strings containing IP addresses and DNS names with which I would like to remove the values beginning with "10." only. The sample data is as follows:

['www.example.com','1.2.3.4','4.3.2.1','example.net','10.1.1.10','10.1.1.11',...]

I thought this would be simple and started with the following:

for v in address:   
    test = re.match('(^\d+\.)',v)
    if test:
        if test.group(1) == '10.':
            address.remove(v)

The "10." addresses were not removed although I didn't receive any errors (and did some t-shooting with "print address.remove(v)" which resulted in "None" for each "10." address. Leads me to believe the regex is wrong but it seems to work other than in this capacity.

So I poked around with re.purge() - this didn't help either but don't think it's a factor in my problem. I also tried using del address[...] to no avail.

Where have I gone wrong?

Thanks very much for your attention.

Upvotes: 3

Views: 27489

Answers (4)

johnsyweb
johnsyweb

Reputation: 141998

One way is to create a new list using a list comprehension and str.startswith():

>>> [a for a in address if not a.startswith('10.')]
['www.example.com', '1.2.3.4', '4.3.2.1', 'example.net', '...']

This avoids using regular expressions and removing items during iteration, but does create a copy.

Upvotes: 3

Reverend Gonzo
Reverend Gonzo

Reputation: 40871

The easy way would be to use list comprehensions:

filtered = [ v for v in address if not v.startswith('10.') ]

Upvotes: 14

Roman Susi
Roman Susi

Reputation: 4199

If would probably make sense to test first that there is really an IP address in question.

Otherwise 10.some-cdn.some-mighty-corp.com will be filtered out.

Related post

Upvotes: 1

Brooks Moses
Brooks Moses

Reputation: 9537

What you've done wrong here is iterating over a list while you're changing the list. That means the iteration gets confused.

See Removing Item From List - during iteration - what's wrong with this idiom? for some suggestions on how to do this correctly.

Upvotes: 1

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