Multiple-replace in python

Question

I do the following for replacing.

import fileinput
for line in fileinput.FileInput("input.txt",inplace=1):
     line = line.replace("A","A'")
     print line,

But I want to do it many replaces.

Replace A with A' , B with BB, C with CX, D with KK, etc.

I can of course do this by repeating the above code many times.

But I guess that will consume a lot of time especially when input.txt is large.

How can I do this elegantly?

Emphasis added

My input is not just a str ABCD.

I need to use input.txt as input and I want to replace every occurrences of A in input.txt to A', every occurrences in input.txt of B to BB, every occurrences of C in input.txt to CX, every occurrences of D in input.txt to KK.

Ashwini Chaudhary · Accepted Answer · 2013-11-02 12:36:44Z

4

Use a mapping dictionary:

>>> map_dict = {'A':"A'", 'B':'BB', 'C':'CX', 'D':'KK'}
>>> strs = 'ABCDEF'
>>> ''.join(map_dict.get(c,c) for c in strs)
"A'BBCXKKEF"

In Python3 use str.translate instead of str.join:

>>> map_dict = {ord('A'):"A'", ord('B'):'BB', ord('C'):'CX', ord('D'):'KK'}
>>> strs = 'ABCDEF'
>>> strs.translate(map_dict)
"A'BBCXKKEF"

edited Nov 2, 2013 at 12:36

answered Nov 2, 2013 at 12:30

Ashwini Chaudhary

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7 Comments

user1849133 Over a year ago

Is it using strs as input? I need to use input.txt as input and I want to replace every occurrences of A in input.txt to A', every occurrences in input.txt of B to BB, every occurrences of C in input.txt to CX, every occurrences of D in input.txt to KK.

Ashwini Chaudhary Over a year ago

@user2604484 Then simply use the text read from input.txt instead of strs.

user1849133 Over a year ago

Hmm I am sorry but I just started to learn python, could you edit the codes in the answer to write the full changes needed including "reading from input.txt"?

Ashwini Chaudhary Over a year ago

@user2604484 Have you tried: line = ''.join(map_dict.get(c,c) for c in line) ?

user1849133 Over a year ago

Thank you! However I got one question. You wrote {'A':"A'", 'B':'BB', 'C':'CX', 'D':'KK'} Here, what replaces A is wrapped by " and ", but what replaces B, C, D are wrapped by ' and '. Why? Should the first one be always " instead of ' ?

|

falsetru · Accepted Answer · 2013-11-02 12:31:59Z

1

Using regular expression:

>>> import re
>>>
>>> replace_map = {
...   'A': "A'",
...   'B': 'BB',
...   'C': 'CX',
...   'D': 'KK',
...   'EFG': '.',
... }
>>> pattern = '|'.join(map(re.escape, replace_map))
>>> re.sub(pattern, lambda m: replace_map[m.group()], 'ABCDEFG')
"A'BBCXKK."

answered Nov 2, 2013 at 12:31

falsetru

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