How to right-align numeric data?

Question

I have some data that I am displaying in 3 column format, of the form:

key: value key: <tab> key: value <tab> key: value.

Here's an example:

p: 1    sl: 10  afy: 4
q: 12   lg: 10  kla: 3
r: 0    kl: 10  klw: 3
s: 67   vw: 9   jes: 3
t: 16   uw: 9   skw: 3
u: 47   ug: 9   mjl: 3
v: 37   mj: 8   lza: 3
w: 119  fv: 8   fxg: 3
x: 16   fl: 8   aew: 3

However, I'd like if the numbers were all right aligned, such as:

a:   1
b:  12
c: 123

How can I do this in Python?

Here is the existing printing code I have:

print(str(chr(i+ord('a'))) + ": " + str(singleArray[i]) + "\t" +
    str(doubleArray[i][0]) + ": " + str(doubleArray[i][1]) + "\t" +
    str(tripleArray[i][0]) + ": " + str(tripleArray[i][1]))

Pat · Accepted Answer · 2012-09-26 02:22:38Z

80

In python 2.6+ (and it's the standard method in 3), the "preferred" method for string formatting is to use string.format() (the complete docs for which can be found here). right justification can be done with

"a string {0:>5}".format(foo)

this will use 5 places, however

"a string {0:>{1}}".format(foo, width)

is also valid and will use the value width as passed to .format().

edited Sep 26, 2012 at 2:22

Pat

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answered Sep 9, 2009 at 22:21

Colin Valliant

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3 Comments

Pat Over a year ago

I don't know why this answer is voted up since it is incorrect - for right-justification/alignment, it is necessary to use "{:>5}" where > indicates right-align (the default for strings is <, or left-aligned). Luckily, the linked-to documentation makes this clear. (EDIT: never mind, I'll just fix the answer and leave this for reference.)

Colin Valliant Over a year ago

It's been upvoted because ">" is the default value of the 'align' field for numbers, and the question was about numbers. You're right, though, that making it explicit is better.

Pat Over a year ago

Mea culpa. I found this question because I was trying to right-align strings, and I didn't read the OP question close enough to catch that only numbers were being printed. Thanks for clarifying.

John Mee · Accepted Answer · 2012-10-02 03:51:50Z

36

In Python 2.5 use rjust (on strings). Also, try to get used to string formatting in python instead of just concatenating strings. Simple example for rjust and string formatting below:

width = 10
str_number = str(ord('a'))
print 'a%s' % (str_number.rjust(width))

edited Oct 2, 2012 at 3:51

John Mee

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answered Sep 9, 2009 at 21:03

ChristopheD

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Comments

Nadia Alramli · Accepted Answer · 2009-09-09 21:29:14Z

27

Use python string formatting: '%widths' where width is an integer

>>> '%10s' % 10
'        10'
>>> '%10s' % 100000
'    100000'

edited Sep 9, 2009 at 21:29

answered Sep 9, 2009 at 21:04

Nadia Alramli

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1 Comment

Mark Over a year ago

For left align use '%-10s' (just adding this because it's the top Google result for left align)

Torkel Bjørnson-Langen · Accepted Answer · 2017-02-13 20:51:41Z

9

In Python 3.6 you can use Literal String Interpolation, which is less verbose and probably more intuitive to use:

width = 5
number = 123
print (f'{number:>{width}}')

Or just:

number = 123
print (f'{number:>5}')

It reuses much of the str.format() syntax.

I guess/hope this will be the prefered way in the future.

answered Feb 13, 2017 at 20:51

Torkel Bjørnson-Langen

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1 Comment

Torkel Bjørnson-Langen Over a year ago

GitHub: Using f-strings style literal string interpolation without Python 3.6

Jochen Ritzel · Accepted Answer · 2009-09-09 21:04:01Z

2

If you know aa upper bound for your numbers, you can format with "%<lenght>d" % n. Given all those calculations are done and in a list of (char, num):

mapping = ((chr(i+ord('a')), singleArray[i]), 
           (doubleArray[i][0],doubleArray[i][1]), 
           (tripleArray[i][0],tripleArray[i][1])
           )
for row in mapping:
   print "%s: %3d" % row

answered Sep 9, 2009 at 21:04

Jochen Ritzel

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