Modify/replace a line in a python file using another python file

Question

I am trying to replace/modify a part of string in a python file from another python file.

The line I am trying to replace in other PY is :

a.setSystemFile('D:/test/f.xml')

I would like to replace the part of this line i.e. the xml path string with different xml path:

Example:

a.setSystemFile('C:/try/X.xml')

My code looks like:

with open('script.py') as f:  lines = f.read().splitlines()
with open('script.py', 'w') as f:

    for line in lines:
      if line.startswith('a.setSystemFile'):

        f.write(line.replace('D:/test/f.xml','C:/try/X.xml')

This however, renders the file empty and only writes C:/try/X.xml. Is there a way to preserve the original content at the same time replace just the XML path string like in above example.

Any help would be appreciated. Thanks.

Answer 1

You forgot to do something if the line doesn't start with that text.

for line in lines:
  if line.startswith('a.setSystemFile'):
    f.write(line.replace('D:/test/f.xml','C:/try/X.xml'))
  else:
    f.write(line)

Also, might I suggest just using sed for this?