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.
This question is related to
python
string
string-formatting
pad
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 '
Just remove the 0 and it will add space instead:
>>> print "'%6d'"%4
You could do it using list comprehension, this'd give you an idea about the number of spaces too and would be a one liner.
"hello" + " ".join([" " for x in range(1,10)])
output --> 'hello '
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,
)
Which results in (you guessed it):
'Hi '
And for all these, you can use python 3.6 f-strings:
message = 'Hi'
fill = ' '
align = '<'
width = 16
f'{message:{fill}{align}{width}}'
And of course the result:
'Hi '
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.
A nice trick to use in place of the various print formats:
(1) Pad with spaces to the right:
('hi' + ' ')[:8]
(2) Pad with leading zeros on the left:
('0000' + str(2))[-4:]
You can try this:
print "'%-100s'" % '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.
For a flexible method that works even when formatting complicated string, you probably should use the string-formatting mini-language, using either the str.format()
method
>>> '{0: <16} StackOverflow!'.format('Hi') # Python >=2.6
'Hi StackOverflow!'
of f-strings
>>> f'{"Hi": <16} StackOverflow!' # Python >= 3.6
'Hi StackOverflow!'
you can also center your string:
'{0: ^20}'.format('nice')
As of Python 3.6 you can just do
>>> strng = 'hi'
>>> f'{strng: <10}'
with literal string interpolation.
Or, if your padding size is in a variable, like this (thanks @Matt M.!):
>>> to_pad = 10
>>> f'{strng: <{to_pad}}'
Use Python 2.7's mini formatting for strings:
'{0: <8}'.format('123')
This left aligns, and pads to 8 characters with the ' ' character.
Correct way of doing this would be to use Python's format syntax as described in the official documentation
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!
Source: Stackoverflow.com