Replacing a word in a text file with a value using python

Question

I have been trying to replace a word in a text file with a value (say 1), but my outfile is blank.I am new to python (its only been a month since I have been learning it).

My file is relatively large, but I just want to replace a word with the value 1 for now. Here is a segment of what the file looks like:

NAME SECOND_1

ATOM 1 6 0 0 0 # ORB 1

ATOM 2 2 0 12/24 0 # ORB 2

ATOM 3 2 12/24 0 0 # ORB 2

ATOM 4 2 0 0 4/24 # ORB 3

ATOM 5 2 0 0 20/24 # ORB 3

ATOM 6 2 0 0 8/24 # ORB 3

ATOM 7 2 0 0 16/24 # ORB 3

ATOM 8 6 0 0 12/24 # ORB 1

ATOM 9 2 12/24 0 12/24 # ORB 2

ATOM 10 2 0 12/24 12/24 # ORB 2

#1

#2

#3

I want to first replace the word ATOM with the value 1. Next I want to replace #ORB with a space. Here is what I am trying thus far.

input = open('SECOND_orbitsJ22.txt','r')
 output=open('SECOND_orbitsJ22_out.txt','w')
for line in input:
    word=line.split(',')
    if(word[0]=='ATOM'):
        word[0]='1'
        output.write(','.join(word))

Can anyone offer any suggestions or help? Thanks so much.

One thing you should make clear for better answers: do you want to replace all occurrences of "ATOM" in your file (as suggested by your question text) or only those that appear at the beginning of the line (as suggested by your code)? — Ray Toal
– Ray Toal, Commented Jun 22, 2012 at 22:55

Lev Levitsky · Accepted Answer · 2012-06-22 21:17:51Z

6

The problem is that there's no comma after ATOM in the input, so word[0] doesn't equal ATOM. You should be splitting on spaces, not commas.

You could also just use split() without arguments.

Since you only do output.write when a match is found, the output stays empty.

P.S. Try to use with statements when opening files:

with open('SECOND_orbitsJ22.txt','r') as input,
    open('SECOND_orbitsJ22_out.txt','w') as output:
   ...

Also, Alexander suggests the right tool for replacement: str.replace. However, use it with caution as it's not position-aware. re.sub is a more flexible alternative.

answered Jun 22, 2012 at 21:17

Lev Levitsky

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Comments

georg · Accepted Answer · 2012-06-23 11:16:57Z

4

Use replace.

line.replace("ATOM", "1").replace("# ORB", " ")

Untested code:

input  = open('inp.txt', 'r')
output = open('out.txt', 'w')
clean  = input.read().replace("ATOM", "1").replace("# ORB", " ")
output.write(clean)

Working example.

edited Jun 23, 2012 at 11:16

georg

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answered Jun 22, 2012 at 21:19

Alexander

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6 Comments

Jamde Jam Over a year ago

Where would I put line.replace("ATOM","1") in the code I posted? Or would it be a different code? Sorry I am new to python.

Joran Beasley Over a year ago

input = open(file); output = input.read().replace("ATOM",1) should replace all occurrances in file ... you dont need to evaluate each line

Jamde Jam Over a year ago

It didn't change anything in the outfile.

Alexander Over a year ago

@JamdeJam, I can see it working here (without reading from a file though)

Jamde Jam Over a year ago

@ Alexander..Thank you so much! It works great! Now I am going to try and create a comma delimted file with this..(Hopefully I can do this). Thanks again!

|

larissa · Accepted Answer · 2012-06-22 21:18:43Z

1

Based on the file segment you've pasted here, you'll want to split each line on a space, rather than a comma. If there are no commas, line.split(',') has no effect, and word[0] is empty. Your output file is empty because you are never writing to it, as ATOM will never be equal to the empty string.

answered Jun 22, 2012 at 21:18

larissa

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