如何在python中几个文件的某些行的末尾添加一个字符串

Question

I have several files with .msh format and want to add a string at the end of some lines of them using python. Name of my files are mod0.msh , mod1.msh , mod2.msh and so on. Each file has thousands of lines but these is how some first lines look like:

$MeshFormat
2.2 0 8
$EndMeshFormat
$PhysicalNames
13
1 10 "W_1"
1 11 "W_2"
2 8 "fault2"
2 9 "fault1"
2 12 "in"
...

I want to add another string ( new_added_string ) at the end of some lines. These lines are:

adding_str=[6,7,8,9]

I tried the following code for only two files but it did not give me what I wanted. I want to also export modified files with the same format of my original files ( .msh ):

for idx in range(2) # 2 means I have two files:
    with open('changed_{}'.format(idx), 'a') as fout:
        with open('mod{}.msh'.format(idx), 'r') as fin:
            lines = fin.readline()
        for i, line in enumerate (lines):
            if i in exp:
                fout.write(' new_added_string')
            else:
                fout.write(line)

Finally, after adding the string to mentioned line numbers, my file will look like:

$MeshFormat
2.2 0 8
$EndMeshFormat
$PhysicalNames
13
1 10 "W_1" new_added_string
1 11 "W_2" new_added_string
2 8 "fault2" new_added_string
2 9 "fault1" new_added_string
2 12 "in"
...

Answer 1

I fixed some bugs:

• for idx in range(2) missing :
• lines = fin.readline() should be readlines , otherwise you only read first line.
• you should output line+'new_added_string' , rather than only output 'new_added_string'

code:

adding_str = [i-1 for i in [6,7,8,9]]
for idx in range(2): # 2 means I have two files:
    with open('changed_{}.txt'.format(idx), 'a') as fout:
        with open('mod{}.msh'.format(idx), 'r') as fin:
            lines = fin.readlines()
        for i, line in enumerate (lines):
            if i in adding_str:
                fout.write(line.replace("\n","") + ' new_added_string\n')
            else:
                fout.write(line)

change_0.txt file result:

$MeshFormat
2.2 0 8
$EndMeshFormat
$PhysicalNames
13
1 10 "W_1" new_added_string
1 11 "W_2" new_added_string
2 8 "fault2" new_added_string
2 9 "fault1" new_added_string
2 12 "in"

Answer 2

Are you aware of the fileinput package for editing files line-wise? Using this and handling the linebreaks might help:

from fileinput import FileInput


adding_str = [6, 7, 8, 9]

for idx in range(2):
    with FileInput(f'mod{idx}.msh', inplace=True, backup='.bak') as in_file:
        for i, line in enumerate(in_file, start=1):
            print(
                line.rstrip(),
                end=' new_added_string\n' if i in adding_str else '\n'
            )

Of course, the in-place modification is not necessary, just a feature one may use.