how to map the string using python

this is my code :

a= ''' ddwqqf{x}'''
def b():
    ...

c=b(a,{'x':'!!!!!'})
print c

i want to get ddwqqf!!!!! ,

so how to create the b function ,

thanks

updated:

but how to do this thing :

a= ''' ddwqqf{x},{'a':'aaaa'}'''

c = a.format(x="!!!!!")

d= open('a.txt','a')
d.write(c)

it show error :

Traceback (most recent call last):
  File "d.py", line 8, in <module>
    c = a.format(x="!!!!!")
KeyError: "'a'"

updated2:

this is the string:

'''
{
    'skill': {x_1},
    'power': {x_2},
    'magic': {x_3},
    'level': {x_4},
    'weapon': {
        0 : {
            'item': {
                'weight': 40,
                'target': 1,
                'defence': 100,
                'name': u'\uff75\uff70\uff78\uff7f\uff70\uff84',
                'attack': 100,
                'type': 1
            },
        },
        1 : {
            'item': {
                'weight': 40,
                'target': 1,
                'defence': 100,
                'name': u'\uff75\uff70\uff78\uff7f\uff70\uff84',
                'attack': 100,
                'type': 1
            },
        },
        2 : {
            'item': {
                'weight': 40,
                'target': 1,
                'defence': 100,开发者_运维百科
                'name': u'\uff75\uff70\uff78\uff7f\uff70\uff84',
                'attack': 100,
                'type': 1
            },
        }
       ......
    }
}
'''

Try

def b(a, d):
    return a.format(**d)

This works in Python 2.6 or above. Of course you would not need to define a function for this:

a = " ddwqqf{x}"
c = a.format(x="!!!!!")

will be enough.

Edit regarding your update:

a = " ddwqqf{x},{{'a':'aaaa'}}"

to avoid substitutions for the second pair of braces.

Another Edit: I don't really know where your string comes from and what's the context of all this. One solution might be

import re
d = {"x_1": "1", "x_2": "2", "x_3": "3", "x_4": "4"}
re.sub(r"\{([a-z_0-9]+)\}", lambda m: d[m.group(1)], s)

where s is your string.