Adding spaces to items in list (Python)

Question

I'm a Python noob and I need some help for a simple problem.

What I need to do is create a list with 3 items and add spaces before and after every item.

For example: l1 = ['a', 'bb', 'c']
should be transformed into: [' a ',' bb ',' c ']

I was trying to write something like this:

lst = ['a', 'bb', 'c']
for a in lst:
    print '  a  '

...and so on for the other elements, but I get a syntax error. Can anyone suggest me a working way to do this? Thanks.

Solution 1

As always, use a list comprehension:

lst = [' {0} '.format(elem) for elem in lst]

This applies a string formatting operation to each element, adding the spaces. If you use python 2.7 or later, you can even omit the 0 in the replacement field (the curly braces).

Solution 2

[ ' {} '.format(x) for x in lst ]

EDIT for python 3.6+:

you can use f-strings instead, see docs: https://www.python.org/dev/peps/pep-0498/

the example above would look like:

[ f' {x} ' for x in lst ]

Solution 3

lst = ['a', 'bb', 'c']  
lst = [' ' + x + ' ' for x in lst]

Solution 4

In [44]: l1 = ['a', 'bb', 'c']

In [45]: [' %s '%x for x in l1]
Out[45]: [' a ', ' bb ', ' c ']

Solution 5

Indent your python code first! And then:

lst = ['a', 'b', 'c']
lst2 = [' ' + a + ' ' for a in lst]
print lst2

View more solutions

Comments

[Burhan Khalid]

This will give you ValueError: zero length field name in format

[Martijn Pieters]

@BurhanKhalid: No it won't. Not in Python 2.7 where I tried it in any case.

[Gareth Latty]

@BurhanKhalid <2.7, yes. There make it ' {0} '. Pre 2.7, automatically numbering items wasn't possible.

[Burhan Khalid]

' {0} '.format(x) would work in all versions where .format() is supported, hence a better answer.

[Martijn Pieters]

You'd be better off using the .format() method, or at a pinch the % string formatting operator, instead of concatenation. It is much more efficient.

[Martijn Pieters]

You'd be better off using the .format() method, or at a pinch the % string formatting operator, instead of concatenation. It is much more efficient.

[Anton Beloglazov]

You can just replace ['a', 'bb', 'c'] with any other list of strings, or with a variable containing a list (e.g., your lst).

[test123]

This worked perfectly for every string I put in, thank you very much!

[Anton Beloglazov]

I agree, using .format() is a more efficient approach in terms of performance.

[test123]

Thank you for the explanation, perfect!