How to write an new line and string after the first occurrence of a string in in an file Python

Question

I would like to write an new line and string after the first the first occurrence of a string in Python For example my text file is like:

123456
example string<random>
asdfg
zxc
example string<random>

I would like it to change to

123456
example string<random>
Python inputted string
asdfg
zxc
example string<random> <- Stays the same

I think maybe it could be useful if you could mention the bigger picture of what you're trying to achieve here. The task seems oddly specific that maybe there's a better way of doing it — sshashank124, Apr 07 '18 at 14:51
`mutable_seq = list(string); mutable_seq.insert(mutable_seq.index(pattern) + 1, 'inserted string'); new_string = ''.join(mutable_seq)` — mental, Apr 07 '18 at 14:56

shahaf · Accepted Answer · 2018-04-07T15:20:03.573

1

read lines from file

lines = []
with open(file_name, 'r') as f:
  for line in f:
    lines.append(line)

with open(file_name, 'w+') as f:
  flag = True
  for line in lines:
    f.write(line)
    if line.startswith("example string") and flag:
      f.write("what ever\n")
      flag = False

input file

123456
example string<random>
asdfg
zxc
example string<random>

output file

123456
example string<random>
what ever
asdfg
zxc
example string<random>

edited Apr 07 '18 at 15:20

answered Apr 07 '18 at 14:52

shahaf

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I did that but the result is an blank text file – Apr 07 '18 at 14:58
@projectuser, provided more specific code... – shahaf Apr 07 '18 at 15:07
That does not allow for – Apr 07 '18 at 15:12
1

You can fix it by changing line 10 to `if line.find("example string") and flag:` – Apr 07 '18 at 15:18
@projectuser then replace `if line.strip() == "example string"` with `if line.startswith("example string")` – shahaf Apr 07 '18 at 15:19

How to write an new line and string after the first occurrence of a string in in an file Python

1 Answers1