Remove all lines that start with a number using python

Question

I am trying to remove all lines in a file that starts with numbers. I came up with that block of code below but it's not working.

output = open("/home/test1/Desktop/diff2.txt", "w")

with open("/home/test1/Desktop/diff.txt") as input:
    for line in input:
    if not line.lstrip().isdigit():
        output.write(line)
        print(line)

    input.close()
    output.close()
    exit();

It still ends up printing all lines that start with numbers in the output file

Answer 1

You are calling is_digit on the whole line, which will return True only if the line consists entirely of digits.

with open('input.txt') as inp, open('output.txt', 'w') as out:
  out.write(''.join(l for l in inp if l[0] not in '123456789'))

Answer 2

The lstrip().isdigit() doesn't check the first char in your line is a digit. You should take the first char (if the line has chars) and check isdigit() on that char:

if line == '' or not line[0].isdigit():
    output.write(line)

Answer 3

This following script works fine on my quick test case:

output = open("test.out", "w")

with open("test.in") as input:
    for line in input:
        if not line.lstrip()[0].isdigit():
            output.write(line)
            print(line)

output.close()

With input:

1test
2test
hello
3test
world
4something

Gives output:

hello
world