How can I fill out a Python string with spaces?


Keywords:python 


Question: 

I want to fill out a string with spaces. I know that the following works for zero's:

>>> print  "'%06d'"%4
'000004'

But what should I do when I want this?:

'hi    '

of course I can measure string length and do str+" "*leftover, but I'd like the shortest way.


12 Answers: 

You can do this with str.ljust(width[, fillchar]):

Return the string left justified in a string of length width. Padding is done using the specified fillchar (default is a space). The original string is returned if width is less than len(s).

>>> 'hi'.ljust(10)
'hi        '


Unless you need to support Python 2.5, you can (and probably should) use the string-formatting mini-language, like so:

'{0: <16}'.format('Hi')


You can try this:

print "'%-100s'" % 'hi'


The new(ish) string format method lets you do some fun stuff with nested keyword arguments. The simplest case:

>>> '{message: <16}'.format(message='Hi')
'Hi             '

If you want to pass in 16 as a variable:

>>> '{message: <{width}}'.format(message='Hi', width=16)
'Hi              '

If you want to pass in variables for the whole kit and kaboodle:

>>> '{message:{fill}{align}{width}}'.format(message='Hi', fill=' ', align='<', width=16)
'Hi              '


Use str.ljust():

>>> 'Hi'.ljust(6)
'Hi    '

You should also consider string.zfill(), str.ljust() and str.center() for string formatting. These can be chained and have the 'fill' character specified, thus:

>>> ('3'.zfill(8) + 'blind'.rjust(8) + 'mice'.ljust(8, '.')).center(40)
'        00000003   blindmice....        '

These string formatting operations have the advantage of working in Python v2 and v3.

Take a look at pydoc str sometime: there's a wealth of good stuff in there.



Correct way of doing this would be to use Python's format syntax as described in the official docummentation

For this case it would simply be:
'{:10}'.format('hi')
which outputs:
'hi '

Explanation:

format_spec ::=  [[fill]align][sign][#][0][width][,][.precision][type]
fill        ::=  <any character>
align       ::=  "<" | ">" | "=" | "^"
sign        ::=  "+" | "-" | " "
width       ::=  integer
precision   ::=  integer
type        ::=  "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"

Pretty much all you need to know is there ^.

Update: as of python 3.6 it's even more convenient with literal string interpolation!

foo = 'foobar'
print(f'{foo:10} is great!')
# foobar     is great!


you can also center your string:

'{0: ^20}'.format('nice')


Use Python 2.7's mini formatting for strings:

'{0: <8}'.format('123')

This left aligns, and pads to 8 characters with the ' ' character.



Just remove the 0 and it will add space instead:

>>> print  "'%6d'"%4


Wouldn't it be more pythonic to use slicing?

For example, to pad a string with spaces on the right until it's 10 characters long:

>>> x = "string"    
>>> (x + " " * 10)[:10]   
'string    '

To pad it with spaces on the left until it's 15 characters long:

>>> (" " * 15 + x)[-15:]
'         string'

It requires knowing how long you want to pad to, of course, but it doesn't require measuring the length of the string you're starting with.



It looks like in Python 3.6 you can just do

>>> strng = 'hi'
>>> f'{strng: <10}'

with literal string interpolation.



+= can be used to append to string

>>> string = 'hi'
>>> for s in range(0,5):
...    string += ' '
... 
>>> string
'hi          '