use variable to specify format in python

Question

I want to format a string to a fixed width

If I use the following statement:

"{0:<8}".format(str(size)) #This one works

However,

# This one gives Invalid conversion specification
"{0:<width}".format(str(size))

Is there anyway to use a variable to format a string?

You could chain multiple formats together, but that would be ugly. Another way would be to just append to a string, or use one of the other ways to string format in addition to this. — Rob Foley
– Rob Foley, Commented Jul 1, 2015 at 17:51

LittleQ · Accepted Answer · 2015-07-01 18:03:57Z

6

Solution 1:
Use width to generate a string {0:<8} first

width = 8
("{0:<%d}"%width).format(s)

Solution 2:
Nested format:

"{0:<{1}}".format(s, width)

Named format maybe more readable:

"{string:<{width}}".format(string=s, width=width)

Solution 3:
Another way to translate {0:<8}: .ljust(8)

"{0}".format(s.ljust(width))

I choose 3. when
1) dealing with other encodings in i18n
2) print pretty

print 'a'.rjust(10, '-')
---------a

answered Jul 1, 2015 at 17:52

LittleQ

1,9251 gold badge14 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

TigerhawkT3 · Accepted Answer · 2015-07-01 17:52:09Z

2

It needs the actual value, not the string 'width'.

str(width).join(("{0:<", "}")).format(str(size))

answered Jul 1, 2015 at 17:52

TigerhawkT3

49.5k6 gold badges66 silver badges101 bronze badges