Question

I used the following sed command to find and replace an old string with a new one:

  cmd = "sed -i 's/"+oldstr+"/"+newstr+"/'"+ "path_to/filename" #change the string in the file
  os.system(cmd) # am calling the sed command in my python script

But i get this error:

sed: -e expression #1, char 8: unterminated `s' command

Can someone tell me what is wrong with my sed command?
Or is anything wrong in the way I have given the file name?

Update:
echo of that command:
sed -i ‘s/6.9.28
/6.9.29/’ dirname/filename

Answer 1

Without calling sed

with open("path_to/filename") as f:
    file_lines = f.readlines()
    new_file = [line.replace(oldstr,newstr) for line in file_lines]

open("path_to/filename","w").write(''.join(new_file))

EDIT:

Incorporating Joran’s comment:

with open("path_to/filename") as f:
    file = f.read()
    newfile = file.replace(oldstr,newstr)

open("path_to/filename","w").write(newfile)

or even

with open("path_to/filename") as f:
    open("path_to/filename","w").write(f.read().replace(oldstr,newstr))