Replacing a part of certain line # with input from another file

I need to replace the numbers(only) from line # 21 to the new numbers from another file
example 74,9,7,114,71,101,10,24,79

I have tried:

with open('', 'a') as f1:      # screenshot file

    for line in open('daysremaining.txt'):   # file containing new numbers

        if 'days_remaining = ' in line:


to no vail.
suggestions are greatly appreciated
thank you,
python 3.6 user

Opening for appending will do just that, let you append, i.e. add new stuff to the end of a file.

What you are actually doing is iterating over the lines in ‘daysremaining.txt’ and then appending to ‘’ if any line that’s in ‘daysremaining.txt’ contains 'days_remaining = '.

What you need to do is copy lines from the original file to a new file, making any changes in the process:

with open('') as input_file:
    with open('', 'w') as output_file:
        for line in input_file:
            if 'days_remaining = ' in line:
                # Make the changes to the line.


# Now you can replace the old file with the new file.

thank you very much for your suggestion.

I was able to do what I wanted with the following:

	with contextlib.redirect_stdout(None):
		with open('daysremaining.txt') as f:
			line = f.readline()
		print (line)
		print (line[0])

	with contextlib.redirect_stdout(None):
		with open('') as f:
			data = f.readlines()
		print (data)
		print (data[0]) 
		newdata = "	days_remaining = "
		newdata2 = (line)
		data[28] = str(newdata) + str(newdata2) 

	with open("", 'w') as f:
		f.writelines( data ) 

thanks again,
python 3.6 user