Remove an integer from a list python

to remove the first two items of a list, you can do

list = list[2:]

Actually, that does not remove items from list. Rather, it creates a new list that excludes the first two items of the original list and assigns it to list. The original list is unaltered.
The distinction between altering a list and creating a new list is significant. Observe the behavior of the following code, and refer to the included comments:

list_a = [1, 2, 3, 4, 5, 6, 7] list_b = list_a # Now list_a and list_b refer to the same list print[list_a] print[list_b] # The following alters list_a and list_b, since they refer to the same list list_a.append[8] print[list_a] print[list_b] # Assign a new list to list_a that excludes the first two items list_a = list_a[2:] # Now list_a and list_b refer to different lists print[list_a] print[list_b]

Output:

[1, 2, 3, 4, 5, 6, 7] [1, 2, 3, 4, 5, 6, 7] [1, 2, 3, 4, 5, 6, 7, 8] [1, 2, 3, 4, 5, 6, 7, 8] [3, 4, 5, 6, 7, 8] [1, 2, 3, 4, 5, 6, 7, 8]>>> a = list['abcdefghijklmnopqrstuvwxyz'] >>> def foo[x]: bar = x[:] del[x[7:17]] return bar >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> Silliness>>> def foo[x]: bar = x[:] n = len[x] // 2 del[x[n-1:n+1]] return bar >>> a = list['abcdefghijklmnopqrstuvwxyz'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'g', 't', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'f', 'u', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'f', 'u', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'e', 'v', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'e', 'v', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'd', 'w', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'd', 'w', 'x', 'y', 'z'] >>> a ['a', 'b', 'c', 'x', 'y', 'z'] >>> foo[a] ['a', 'b', 'c', 'x', 'y', 'z'] >>> a ['a', 'b', 'y', 'z'] >>> foo[a] ['a', 'b', 'y', 'z'] >>> a ['a', 'z'] >>> foo[a] ['a', 'z'] >>> a [] >>>

Ive bookmarked your post and given it some thought. Cant say this is derivative, but it stems from the root

>>> a = list['abcdefghijklmnopqrstuvwxyz'] >>> a[7:17] == a[-19:-9] True >>>

Most of those trees may exist where you are, but in our parts I feel joy whenever I see a river birch. The rest are not native to our region. We have slightly less rare stands of cottonwood, but mostly its aspen, willow, wild-berry [prickly rose, chokecherry, saskatoon]. There are no great trees on the prairies.

During the railroad era of a century ago they introduced spruce from the Jasper region, so we have lots of them around, but all human planted.

All those evergreens were put there by humans.

Not so easy to see, now, though,

I didnt print the pop of the list

Ultimately, as list methods go, that is one of the key roles that pop serves It gives us the value it just removed. If the value is of no importance, then use another method, would be my leaning.

The del function is quick and ideal. It removes the slice of values and Bobs yer uncle.

list.remove is also an option, but it looks for values, not indices.

Okay, now lets get down to understanding your code.

We are given a list of some length. Now we are to iterate a range the length of the list. That will give us indices with which to poll the list. If the value at that index is greater than three then pop that index. Print the list at that point [or at the end, cant tell].

Heres the problem When we remove an element from a list, it gets shortened by one. The range were iterating over doesnt, so, at some point we will reach an index that is out or range since the list is shorter and that index no longer exists.

Here are three ways. Uncomment each in turn to try them out.

lst = [1, 2, 3, 4] #new_lst = lst[:] #new_lst = lst.copy[] new_lst = list[lst] new_lst.remove[3] # this should look up the value 3 in new_list and remove it print[new_lst] print[lst]

Output [for any of the three options shown]:

[1, 2, 4] [1, 2, 3, 4]

If your original list contains mutable objects [i.e., lists], and you experimant a bit, you will discover some interesting, possibly unexpected behavior. To get around it, you will need to use copy.deepcopy:

lst = [1, [2, 3, 4]] new_lst = lst[:] print[new_lst[1]] # sublist new_lst[1].remove[3] # this should look up the value 3 in new_list and remove it print[new_lst] # [1, 2, 4] print[lst] # [1, 2, 4] print["Now using deepcopy"] import copy lst = [1, [2, 3, 4]] new_lst = copy.deepcopy[lst] print[new_lst[1]] new_lst[1].remove[3] # this should look up the value 3 in new_list and remove it print[new_lst] # [1, 2, 4] print[lst] # [1, 2, 4]

Output:

[2, 3, 4] # here is the sublist [1, [2, 4]] [1, [2, 4]] # original list affected Now using deepcopy [2, 3, 4] [1, [2, 4]] [1, [2, 3, 4]] # original list unaffected

Addendum with respect to copying objects

When we want to be sure that our copy is indeed a copy, and not a reference to the original. check its id.

>>> p = [1, 2, 3] >>> id[p] 140669632471176 >>> q = p > id[q] 140669632471176 >>>

If the ids match, its not a copy, but a reference, only.

>>> id[199] 140669688098336 >>> x = 199 >>> id[x] 140669688098336 >>>

Above we can see how Python will give a number value an id. There is only ever one value in memory of any one number, never more. When we assign that number to a variable, it still has the same id.

That will be the case no matter what structure we use the number in.

>>> u = [1, 9, 19, 99, 199] >>> id[u[4]] 140669688098336 >>> v = {'one': 1, 'one-ninety-nine': 199} >>> id[v['one-ninety-nine']] 140669688098336 >>>

As for copies, that is true copies, or clones,

>>> id[u] 140669625218312 >>> w = u.copy[] >>> id[w] 140669625233288 >>> id[w[4]] 140669688098336 >>>

Note the last id. Granted the two lists are unique, now, but any values they have in common ARE the same value in memory.

This parallels through all objects, regardless their data type. There is only ever one of any one value in memory.