Question

Possible Duplicate:
Search and replace a line in a file in Python
How do I modify a text file in Python?

I have an input file that I need to rewrite with the different files needed to be modified before running a program. I have tried a variety of the solutions on here but none of them seem to work. I end up just overwriting my file with a blank file

f = open(filename, 'r+')
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.write(text)
f.truncate()
f.close()

Or with that code for instance the name I am changing is different each time I run the program so I need to replace the entire line not just one keyword

Answer 1

A simple way may be to read the text into a string, then concatenate the string with the text you want to write:

infile = open('hey.txt','r+')
content = infile.read()
text = ['foo','bar']
for item in text:
     content +=item  #adds 'foo' on first iteration, 'bar' on second
infile.write(content)
infile.close()

or to change a particular key word:

infile = open('hey.txt','r+')
content = infile.read()
table = str.maketrans('foo','bar')
content = content.translate(table)  #replaces 'foo' with 'bar'
infile.write(content)
infile.close()

or to change by line, you can use readlines and refer to each line as the index of a list:

infile = open('hey.txt','r+')
content = infile.readlines() #reads line by line and out puts a list of each line
content[1] = 'This is a new line\n' #replaces content of the 2nd line (index 1)
infile.write(content)
infile.close()

Maybe not a particularly elegant way to solve the problem, but it could be wrapped up in a function and the ‘text’ variable could be a number of data types like a dictionary, list, etc. There are also a number of ways to replace each line in a file, it just depends on what the criteria are for changing the line (are you searching for a character or word in the line? Are you just looking to replace a line based on where it is in the file?)–so those are also some things to consider.

Edit: Added quotes to third code sample