How to delete line from the file in python

Question

I have a file F, content huge numbers eg F = [1,2,3,4,5,6,7,8,9,...]. So i want to loop over the file F and delete all lines contain any numbers in file say f = [1,2,4,7,...].

F = open(file)
f = [1,2,4,7,...]
for line in F:
    if line.contains(any number in f):
        delete the line in F

Answer 1

You can not immediately delete lines in a file, so have to create a new file where you write the remaining lines to. That is what chonws example does.

Answer 2

It's not clear to me what the form of the file you are trying to modify is. I'm going to assume it looks like this:

1,2,3
4,5,7,19
6,2,57
7,8,9
128

Something like this might work for you:

filter = set([2, 9])
lines = open("data.txt").readlines()
outlines = []
for line in lines:
    line_numbers = set(int(num) for num in line.split(","))
    if not filter & line_numbers:
        outlines.append(line)
if len(outlines) < len(lines):
    open("data.txt", "w").writelines(outlines)

I've never been clear on what the implications of doing an open() as a one-off are, but I use it pretty regularly, and it doesn't seem to cause any problems.

Answer 3

exclude = set((2, 4, 8))           # is faster to find items in a set
out = open('filtered.txt', 'w')
with open('numbers.txt') as i:     # iterates over the lines of a file
    for l in i:
        if not any((int(x) in exclude for x in l.split(','))):
            out.write(l)
out.close()

I'm assuming the file contains only integer numbers separated by ,

Answer 4

Something like this?:

nums = [1, 2]
f = open("file", "r")
source = f.read()
f.close()
out = open("file", "w")
for line in source.splitlines():
    found = False
    for n in nums:
        if line.find(str(n)) > -1:
            found = True
            break
    if found:
        continue
    out.write(line+"\n")
out.close()