如何以固定宽度打印字符串？

I have this code (printing the occurrence of the all permutations in a string)

def splitter(str):
    for i in range(1, len(str)):
        start = str[0:i]
        end = str[i:]
        yield (start, end)
        for split in splitter(end):
            result = [start]
            result.extend(split)
            yield result    

el =[];

string = "abcd"
for b in splitter("abcd"):
    el.extend(b);

unique =  sorted(set(el));

for prefix in unique:
    if prefix != "":
        print "value  " , prefix  , "- num of occurrences =   " , string.count(str(prefix));

I want to print all the permutation occurrence there is in string varaible.

since the permutation aren’t in the same length i want to fix the width and print it in a nice not like this one:

value   a - num of occurrences =    1
value   ab - num of occurrences =    1
value   abc - num of occurrences =    1
value   b - num of occurrences =    1
value   bc - num of occurrences =    1
value   bcd - num of occurrences =    1
value   c - num of occurrences =    1
value   cd - num of occurrences =    1
value   d - num of occurrences =    1

How can I use format to do it?

I found these posts but it didn’t go well with alphanumeric strings:

python string formatting fixed width

Setting fixed length with python

EDIT 2013-12-11 – This answer is very old. It is still valid and correct, but people looking at this should prefer the new format syntax.

You can use string formatting like this:

>>> print '%5s' % 'aa'
   aa
>>> print '%5s' % 'aaa'
  aaa
>>> print '%5s' % 'aaaa'
 aaaa
>>> print '%5s' % 'aaaaa'
aaaaa

Basically:

• the % character informs python it will have to substitute something to a token
• the s character informs python the token will be a string
• the 5 (or whatever number you wish) informs python to pad the string with spaces up to 5 characters.

In your specific case a possible implementation could look like:

>>> dict_ = {'a': 1, 'ab': 1, 'abc': 1}
>>> for item in dict_.items():
...     print 'value %3s - num of occurances = %d' % item # %d is the token of integers
... 
value   a - num of occurances = 1
value  ab - num of occurances = 1
value abc - num of occurances = 1

SIDE NOTE: Just wondered if you are aware of the existence of the itertools module. For example you could obtain a list of all your combinations in one line with:

>>> [''.join(perm) for i in range(1, len(s)) for perm in it.permutations(s, i)]
['a', 'b', 'c', 'd', 'ab', 'ac', 'ad', 'ba', 'bc', 'bd', 'ca', 'cb', 'cd', 'da', 'db', 'dc', 'abc', 'abd', 'acb', 'acd', 'adb', 'adc', 'bac', 'bad', 'bca', 'bcd', 'bda', 'bdc', 'cab', 'cad', 'cba', 'cbd', 'cda', 'cdb', 'dab', 'dac', 'dba', 'dbc', 'dca', 'dcb']

and you could get the number of occurrences by using combinations in conjunction with count().

I find using str.format much more elegant:

>>> '{0: <5}'.format('s')
's    '
>>> '{0: <5}'.format('ss')
'ss   '
>>> '{0: <5}'.format('sss')
'sss  '
>>> '{0: <5}'.format('ssss')
'ssss '
>>> '{0: <5}'.format('sssss')
'sssss'

If you want to align the string to the right use > instead of <:

>>> '{0: >5}'.format('ss')
'   ss'

Edit 1: As mentioned in the comments: the 0 in '{0: <5}' indicates the argument’s index passed to str.format().

Edit 2: In python3 one could use also f-string:

sub_str='s'
for i in range(1,6):
    s = sub_str*i
    print(f'{s:>5}')
    
'    s'
'   ss'
'  sss'
' ssss'
'sssss'

or:

for i in range(1,5):
    s = sub_str*i
    print(f'{s:<5}')
's    '
'ss   '
'sss  '
'ssss '
'sssss'

of note, in some places above, ' ' (single quotation marks) were added to emphasize the width of the printed strings.

Originally posted as an edit to @0x90’s answer, but it got rejected for deviating from the post’s original intent and recommended to post as a comment or answer, so I’m including the short write-up here.

In addition to the answer from @0x90, the syntax can be made more flexible, by using a variable for the width (as per @user2763554’s comment):

width=10
'{0: <{width}}'.format('sss', width=width)

Further, you can make this expression briefer, by only using numbers and relying on the order of the arguments passed to format:

width=10
'{0: <{1}}'.format('sss', width)

Or even leave out all numbers for maximal, potentially non-pythonically implicit, compactness:

width=10
'{: <{}}'.format('sss', width)

Update 2017-05-26

With the introduction of formatted string literals (“f-strings” for short) in Python 3.6, it is now possible to access previously defined variables with a briefer syntax:

>>> name = "Fred"
>>> f"He said his name is {name}."
'He said his name is Fred.'

This also applies to string formatting

>>> width=10
>>> string = 'sss'
>>> f'{string: <{width}}'
'sss       '

format is definitely the most elegant way, but afaik you can’t use that with python’s logging module, so here’s how you can do it using the % formatting:

formatter = logging.Formatter(
    fmt='%(asctime)s | %(name)-20s | %(levelname)-10s | %(message)s',
)

Here, the - indicates left-alignment, and the number before s indicates the fixed width.

Some sample output:

2017-03-14 14:43:42,581 | this-app             | INFO       | running main
2017-03-14 14:43:42,581 | this-app.aux         | DEBUG      | 5 is an int!
2017-03-14 14:43:42,581 | this-app.aux         | INFO       | hello
2017-03-14 14:43:42,581 | this-app             | ERROR      | failed running main

More info at the docs here: https://docs.python.org/2/library/stdtypes.html#string-formatting-operations

>>> print(f"{'123':<4}56789")
123 56789