pythonic way to iterate over part of a list

Question

I want to iterate over everything in a list except the first few elements, e.g.:

for line in lines[2:]:     foo(line) 

This is concise, but copies the whole list, which is unnecessary. I could do:

del lines[0:2] for line in lines:     foo(line) 

But this modifies the list, which isn't always good.

I can do this:

for i in xrange(2, len(lines)):     line = lines[i]     foo(line) 

But, that's just gross.

Better might be this:

for i,line in enumerate(lines):     if i < 2: continue     foo(line) 

But it isn't quite as obvious as the very first example.

So: What's a way to do it that is as obvious as the first example, but doesn't copy the list unnecessarily?

Answer 1

You can try itertools.islice(iterable[, start], stop[, step]):

import itertools for line in itertools.islice(list , start, stop):      foo(line) 

Answer 2

The original solution is, in most cases, the appropriate one.

for line in lines[2:]:     foo(line) 

While this does copy the list, it is only a shallow copy, and is quite quick. Don't worry about optimizing until you have profiled the code and found this to be a bottleneck.