how to replace a line of two words in a file using python

Question

I want to replace a line in a file but my code doesn't do what I want. The code doesn't change that line. It seems that the problem is the space between ALS and 4277 characters in the input.txt. I need to keep that space in the file. How can I fix my code?

A part part of input.txt:

ALS              4277

Related part of the code:

        for lines in fileinput.input('input.txt', inplace=True): 
            print(lines.rstrip().replace("ALS"+str(4277), "KLM" + str(4945)))

Desired output:

KLM              4945

You need to account for the spaces. "ALS"+str(4277) is the same as "ALS4277" — OrderAndChaos
– OrderAndChaos, Commented Oct 20, 2016 at 9:20

cimarie · Accepted Answer · 2016-10-20 09:34:11Z

2

Using the same idea that other user have already pointed out, you could also reproduce the same spacing, by first matching the spacing and saving it in a variable (spacing in my code):

import re

with open('input.txt') as f:
    lines = f.read()

match = re.match(r'ALS(\s+)4277', lines)
if match != None:
    spacing = match.group(1)
    lines = re.sub(r'ALS\s+4277', 'KLM%s4945'%spacing, lines.rstrip())

print lines

answered Oct 20, 2016 at 9:34

cimarie

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3 Comments

OrderAndChaos Over a year ago

I thought about doing this: spaces = " " * 14 then "KLM%s4945" % spaces to make the spaces consistent.

OrderAndChaos Over a year ago

Ha, I swear this question has changed since I answered it.

cimarie Over a year ago

Don't know about the question being changed - I really don't remember whether the OP stated that she/he wanted to keep the spaces or not. I just thought the spaces might vary, so maybe it would be easier to "automatize" the task :)

OrderAndChaos · Accepted Answer · 2016-10-20 09:29:20Z

1

As the spaces vary you will need to use regex to account for the spaces.

import re

lines = "ALS              4277    "
line = re.sub(r"(ALS\s+4277)", "KLM              4945", lines.rstrip())

print(line)

answered Oct 20, 2016 at 9:29

OrderAndChaos

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Comments

acw1668 · Accepted Answer · 2016-10-20 09:52:14Z

0

Try:

with open('input.txt') as f:
    for line in f:
        a, b = line.strip().split()
        if a == 'ALS' and b == '4277':
            line = line.replace(a, 'KLM').replace(b, '4945')
        print(line, end='') # as line has '\n'

edited Oct 20, 2016 at 9:52

answered Oct 20, 2016 at 9:40

acw1668

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