同时提取和替换字符串中的字母

Question

I have a 'string1' with two kinds of positions: the inverse position (identified by position=change) and the direct position (identified by just position=). To make myself clear, take for example letters=abcdef and position=change(1-4). The letters in between the first and the fourth gap, that are bcd, must be extracted, and letter c must be replaced with the number 1. For reasons not to the case, in the inverse position case, it is always the letter c that must be replaced by digit 1. In the direct position case, the replacing is not performed.

I need to do this by a loop, and I have written the code I show you here, but it doesn't work.

string1='*This is an inverse position [position=change(1-4)]in a long sentence\n*This is a direct position [position=2-7] in a long sentence'
import re 
a=re.finditer(r'(\*This).*\]', string1)
for element in a:
    print element.group()

letters='abcdefghijklmno'
b=re.finditer(r'([0-9]+)-([0-9]+)', element.group())
for i in b:
    if element.group().find('change'):
        changedletters=letters[int(i.group(1)) : int(i.group(2))].replace('c', '1')
        print element.group()+changedletters
    else:
        print letters[int(i.group(1)) : int(i.group(2))]

Answer 1

In your code, there is so much wrong:

1. regular expressions are greedy. So your finditer finds the first This and the last position.
2. Your second part of the code is not inside the first loop, so only the last occurence of finditer is processed.
3. The regular expression is not very fault tolerant

Find this:

import re 

LETTERS = 'abcdefghijklmno'

def output_letters(text):
    elements = re.finditer(r'(\*This).*?\[position=(change\()?(\d+)-(\d+)\)?\]', text)
    for element in elements:
        print element.group(0)
        letters = LETTERS[int(element.group(3)):int(element.group(4))]
        if element.group(2):
            letters = letters.replace('c','1')
        print letters


string1='*This is an inverse position [position=change(1-4)]in a long sentence\n*This is a direct position [position=2-7] in a long sentence'
output_letters(string1)