python - Remove trailing newline from the elements of a string list

136
votes

I have to take a large list of words in the form:

['this\n', 'is\n', 'a\n', 'list\n', 'of\n', 'words\n']

and then using the strip function, turn it into:

['this', 'is', 'a', 'list', 'of', 'words']

I thought that what I had written would work, but I keep getting an error saying:

"'list' object has no attribute 'strip'"

Here is the code that I tried:

strip_list = []
for lengths in range(1,20):
    strip_list.append(0) #longest word in the text file is 20 characters long
for a in lines:
    strip_list.append(lines[a].strip())
7
pythonliststrip
Please explain why you are appending 0 to strip_list 19 times then appending your stripped lines. That code has a very bad smell about it. Also if you got that stuff from a file, you should be stripping it on the way in -- building a large list then bashing it into another large list is not a good idea. Also 2, your code should not depend on knowing the length of the longest word/line. Step back a bit -- what are your trying to achieve? What will you do with strip_list? - John Machin
Related How to remove \n from a list element? - Bhargav Rao♦

7 Answers

234
votes

You can either use a list comprehension

my_list = ['this\n', 'is\n', 'a\n', 'list\n', 'of\n', 'words\n']
stripped = [s.strip() for s in my_list]

or alternatively use map():

stripped = list(map(str.strip, my_list))

In Python 2, map() directly returned a list, so you didn't need the call to list. In Python 3, the list comprehension is more concise and generally considered more idiomatic.

128
votes

list comprehension? [x.strip() for x in lst]

67
votes

You can use lists comprehensions:

strip_list = [item.strip() for item in lines]

Or the map function:

# with a lambda
strip_list = map(lambda it: it.strip(), lines)

# without a lambda
strip_list = map(str.strip, lines)
8
votes

This can be done using list comprehensions as defined in PEP 202

[w.strip() for w in  ['this\n', 'is\n', 'a\n', 'list\n', 'of\n', 'words\n']]
3
votes

All other answers, and mainly about list comprehension, are great. But just to explain your error: 

strip_list = []
for lengths in range(1,20):
    strip_list.append(0) #longest word in the text file is 20 characters long
for a in lines:
    strip_list.append(lines[a].strip())

a is a member of your list, not an index. What you could write is this:

[...]
for a in lines:
    strip_list.append(a.strip())

Another important comment: you can create an empty list this way:

strip_list = [0] * 20

But this is not so useful, as .append appends stuff to your list. In your case, it's not useful to create a list with defaut values, as you'll build it item per item when appending stripped strings.

So your code should be like:

strip_list = []
for a in lines:
    strip_list.append(a.strip())

But, for sure, the best one is this one, as this is exactly the same thing:

stripped = [line.strip() for line in lines]

In case you have something more complicated than just a .strip, put this in a function, and do the same. That's the most readable way to work with lists.

2
votes

If you need to remove just trailing whitespace, you could use str.rstrip(), which should be slightly more efficient than str.strip():

>>> lst = ['this\n', 'is\n', 'a\n', 'list\n', 'of\n', 'words\n']
>>> [x.rstrip() for x in lst]
['this', 'is', 'a', 'list', 'of', 'words']
>>> list(map(str.rstrip, lst))
['this', 'is', 'a', 'list', 'of', 'words']
-1
votes
my_list = ['this\n', 'is\n', 'a\n', 'list\n', 'of\n', 'words\n']
print([l.strip() for l in my_list])

Output:

['this', 'is', 'a', 'list', 'of', 'words']