Python find pattern and replace entire line

Question

def replace(file_path, pattern, subst):
   file_path = os.path.abspath(file_path)
   #Create temp file
   fh, abs_path = mkstemp()
   new_file = open(abs_path,'w')
   old_file = open(file_path)
   for line in old_file:
       new_file.write(line.replace(pattern, subst))
   #close temp file
   new_file.close()
   close(fh)
   old_file.close()
   #Remove original file
   remove(file_path)
   #Move new file
   move(abs_path, file_path)

I have this function to replace string in a file. But I can't figure out a good way to replace the entire line where the pattern is found.

For example if I wanted to replace a line containining: "John worked hard all day" using pattern "John" and the replacement would be "Mike didn't work so hard".

With my current function I would have to write the entire line in pattern to replace the entire line.

Are you asking how to do it without changing this code? Because I would think if you can change this code the answer should be pretty straightforward. — kojiro
– kojiro, Commented Oct 21, 2013 at 13:17

Inbar Rose · Accepted Answer · 2015-05-05 08:37:15Z

7

Firstly, you could change this part:

for line in old_file:
    new_file.write(line.replace(pattern, subst))

Into this:

for line in old_file:
    if pattern in line:
        new_file.write(subst)
    else:
        new_file.write(line)

Or you could make it even prettier:

for line in old_file:
    new_file.write(subst if pattern in line else line)

edited May 5, 2015 at 8:37

answered Oct 21, 2013 at 13:15

Inbar Rose

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