Replacing multiple similar strings

问题:

I have the folowing expression:

a = 'x11 + x111 + x1111 + x1'

and I would like to replace the following:

from_ = ['1', '11', '111', '1111']
to = ['2', '22', '333', '3333']

and therefore obtain the following result:

anew = 'x22 + x333 + x3333 + x2'

How can I do this using Python?

This is a similar question to: Python replace multiple strings. However in my case the replaced values are being overwiten by themselves if I use the suggested anwsers in the question. Hence, in the metioned link the result is 'x22 + x222 + x2222 + x2'

回答1:

re.sub from the re library (regex) can be used whenever you need to do multi-value replacements.

re.sub takes in the additional argument of a function, in that function you can make the necessary change. From the documentation

re.sub(pattern, repl, string, count=0, flags=0)

If repl is a function, it is called for every non-overlapping occurrence of pattern. The function takes a single match object argument, and returns the replacement string.

_{(emphasis mine)}

The regex here is simple, i.e, \d+ which implies that you are matching all the groups of digits.

You can utilize the following code snippet to get your desired output

import re

a = 'x11 + x111 + x1111 + x1'

def substitute(matched_obj):
    from_ = ['1', '11', '111', '1111']
    to = ['2', '22', '333', '3333']
    part = matched_obj.group(0)
    if part in from_:
        return to[from_.index(part)]
    return part

anew = re.sub(r'\d+',substitute,a)

After executing the program the value of anew will be x22 + x333 + x3333 + x2 which is the expected answer. `