You can try this:

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

Use str.ljust():

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

You should also consider string.zfill(), str.rjust() 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 f-strings

>>> f'{"Hi": <16} StackOverflow!'  # Python >= 3.6
'Hi               StackOverflow!'

or the str.format() method

>>> '{0: <16} StackOverflow!'.format('Hi')  # Python >=2.6
'Hi               StackOverflow!'

Use Python 2.7’s mini formatting for strings:

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

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

you can also center your string:

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

The 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              '

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.

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}}'

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!

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                 '

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:]

This approach is not recommended in Python but the logic is useful for languages and macros that lack quality text formatting functions. 🙂

TL;DR

text = 'hi'
print(f'{text:10}') # 'hi        '

Longer explanation

Since Python3.6 you can use f-strings literal interpolation.

Variable space:

value = 4
space = 10

# move value to left
print(f'foo {value:<{space}} bar') # foo 4          bar
# move value to right
print(f'foo {value:>{space}} bar') # foo          4 bar
# center value
print(f'foo {value:^{space}} bar') # foo     4      bar

Constant space:

value = 4

# move value to left
print(f'foo {value:<10} bar') # foo 4          bar
# move value to right
print(f'foo {value:>10} bar') # foo          4 bar
# center value
print(f'foo {value:^10} bar') # foo     4      bar

If you want to padd with some other char then space, specify it at the beginning:

value = 4
space = 10
padd = '_'

print(f'foo {value:{padd}^{space}} bar') # foo ____4_____ bar
print(f'foo {value:_^10} bar')           # foo ____4_____ bar