Commenting a pattern of line in a file

I need to comment a set of line which has similar pattern with a unique value on it.

example

a {
1
2 one
3
}


a {
1
2 two
3
}

In the above example I need to comment the entire block. base on the unique value "two" like this.

a {
1
2 one
3
}

#a {
#1
#2 two
#3
#}

The above I'm able to get the block with index line but unable to do a inplace edit or replace. I'm using python2 code:

line = open('file').readlines()
index = line.index('two\n')
abline = int(index)-2
beline = int(abline)+5
for linei in range(abline,beline+1):
    nline = '%s%s' % ("##",line[linei].strip())
    print(nline)

I don't think you can do it inplace. what you can do is read the file first, comment its content and then write into the file. something like this

lines = open('file').readlines()

index = -1

for ind,line in enumerate(lines):
    if 'two' in line:
        index = ind 

commented_lines = ''
for ind,line in enumerate(lines):
    if ind >= index-2 and ind <=index+2:
        commented_lines += '#%s' %line
    else:
        commented_lines += line


with open('file', 'w') as f:
    f.write(commented_lines)

assuming the searched text will always be present in the file.