How to manipulate elements of a list in a single line of code?

[mrstephengross]

I would like to translate the contents of a list. For instance, let's
say I've got a list of strings and I want to append "foo" to each
element. I might do the following;

list1 = ['a', 'b', 'c']
for i in range(0, len(list1)): list1 += 'foo'

Ok, that much works. But what if I don't want to modify the contents
of list1. Instead, I want list2 to hold the modified contents, like
so:

1 list1 = ['a', 'b', 'c']
2 list2 = []
3 for item in list1: list2.append(item + 'foo')

Is there a way to express lines 2-3 sort-of ilke this:

list2 = [ for item in list1: item + 'foo' ]

Any ideas?

Thanks,
--Steve

 

[Dan]

I would like to translate the contents of a list. For instance, let's
say I've got a list of strings and I want to append "foo" to each
element. I might do the following;

list1 = ['a', 'b', 'c']
for i in range(0, len(list1)): list1 += 'foo'

Ok, that much works. But what if I don't want to modify the contents
of list1. Instead, I want list2 to hold the modified contents, like
so:

1 list1 = ['a', 'b', 'c']
2 list2 = []
3 for item in list1: list2.append(item + 'foo')

Is there a way to express lines 2-3 sort-of ilke this:

list2 = [ for item in list1: item + 'foo' ]

Any ideas?

Thanks,
--Steve

You're so close.

list2 = [ item+"foo" for item in list1 ]

-Dan

 

[Ben C]

I would like to translate the contents of a list. For instance, let's
say I've got a list of strings and I want to append "foo" to each
element. I might do the following;

list1 = ['a', 'b', 'c']
for i in range(0, len(list1)): list1 += 'foo'

Ok, that much works. But what if I don't want to modify the contents
of list1. Instead, I want list2 to hold the modified contents, like
so:

1 list1 = ['a', 'b', 'c']
2 list2 = []
3 for item in list1: list2.append(item + 'foo')

Is there a way to express lines 2-3 sort-of ilke this:

list2 = [ for item in list1: item + 'foo' ]

Yes, it's called a "list comprehension", and is many people's favourite
Python feature.

list2 = [x + 'foo' for x in list1]

You can also add a condition

list2 = [x + 'foo' for x in list1 if x != "bar"]

for example.

 

[Paulo da Costa]

1 list1 = ['a', 'b', 'c']
2 list2 = []
3 for item in list1: list2.append(item + 'foo')

Is there a way to express lines 2-3 sort-of ilke this:

list2 = [ for item in list1: item + 'foo' ]

list2 = [ item + 'foo' for item in list1 ]

Paulo

 

[D'Arcy J.M. Cain]

1 list1 = ['a', 'b', 'c']
2 list2 = []
3 for item in list1: list2.append(item + 'foo')

Is there a way to express lines 2-3 sort-of ilke this:

list2 = [ for item in list1: item + 'foo' ]

You almost have it.

list2 = [item + 'foo' for item in list1]

 

[mrstephengross]

Yes, it's called a "list comprehension", and is many people's favourite

Awesome!

Thanks,
--Steve