Can this be done with list comprehension?

[Karlo Lozovina]

This is what I'm trying to do (create a list using list comprehesion, then
insert new element at the beginning of that list):

result = [someFunction(i) for i in some_list].insert(0, 'something')

But instead of expected results, I get None as `result`. If instead of
calling `insert` method I try to index the list like this:

result = [someFunction(i) for i in some_list][0]

It works as expected. Am I doing something wrong, or I can't call list
methods when doing list comprehension?

P.S.
In case you're wondering, it has to be done in one line .

 

[Gary Herron]

This is what I'm trying to do (create a list using list comprehesion, then
insert new element at the beginning of that list):

result = [someFunction(i) for i in some_list].insert(0, 'something')

But instead of expected results, I get None as `result`. If instead of
calling `insert` method I try to index the list like this:

result = [someFunction(i) for i in some_list][0]

It works as expected. Am I doing something wrong, or I can't call list
methods when doing list comprehension?

The problem is that list methods like insert do not return a list --
they modify it in place. If you do
a = [1,2,3]
a.insert(0, 'something')
then a will have the results you expect, but if you do
b = a.insert(0,'something')
you will find b to be None (although a will have the expected list).

 

[Karlo Lozovina]

The problem is that list methods like insert do not return a list --
they modify it in place. If you do
a = [1,2,3]
a.insert(0, 'something')
then a will have the results you expect, but if you do
b = a.insert(0,'something')
you will find b to be None (although a will have the expected list).

I figured that out few minutes ago, such a newbie mistake . The fix I
came up with is:

result = ['something'] + [someMethod(i) for i in some_list]

Are there any other alternatives to this approach?

 

[John Machin]

This is what I'm trying to do (create a list using list comprehesion, then
insert new element at the beginning of that list):

result = [someFunction(i) for i in some_list].insert(0, 'something')

result = ['something'] + [someFunction(i) for i in some_list]

 

[Terry Reedy]

| I figured that out few minutes ago, such a newbie mistake . The fix I
| came up with is:
|
| result = ['something'] + [someMethod(i) for i in some_list]
|
| Are there any other alternatives to this approach?

result = [something]
result.extend(someMethod(i) for i in some_list)

avoids creating and deleting an intermediate list

 

[Lie]

| I figured that out few minutes ago, such a newbie mistake . The fix I
| came up with is:
|
|  result = ['something'] + [someMethod(i) for i in some_list]
|
| Are there any other alternatives to this approach?

result = [something]
result.extend(someMethod(i) for i in some_list)

avoids creating and deleting an intermediate list

or:
result = ['something'].extend(someMethod(i) for i in some_list)

it also avoids intermediate list and is one line.

 

[Maric Michaud]

Le Sunday 08 June 2008 02:27:54 Terry Reedy, vous avez écrit :

| I figured that out few minutes ago, such a newbie mistake . The fix I
| came up with is:
|
| result = ['something'] + [someMethod(i) for i in some_list]
|
| Are there any other alternatives to this approach?

result = [something]
result.extend(someMethod(i) for i in some_list)

avoids creating and deleting an intermediate list

A one liner, though it's a bit lispy :

list(itertools.chain((something,), (someMethod(i) for i in some_list)))