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.

Answer 1

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.

PS 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.

Answer 2

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 .

Answer 3

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.