[python] Copying from one text file to another using Python

I would like to copy certain lines of text from one text file to another. In my current script when I search for a string it copies everything afterwards, how can I copy just a certain part of the text? E.g. only copy lines when it has "tests/file/myword" in it?

current code:

#!/usr/bin/env python
f = open('list1.txt')
f1 = open('output.txt', 'a')

doIHaveToCopyTheLine=False

for line in f.readlines():

    if 'tests/file/myword' in line:
        doIHaveToCopyTheLine=True

    if doIHaveToCopyTheLine:
        f1.write(line)

f1.close()
f.close()

If all of that did not work try this.

with open("hello.txt") as f:
with open("copy.txt", "w") as f1:
    for line in f:
        f1.write(line)

f=open('list1.txt')  
f1=open('output.txt','a')
for x in f.readlines():
    f1.write(x)
f.close()
f1.close()

this will work 100% try this once

Just a slightly cleaned up way of doing this. This is no more or less performant than ATOzTOA's answer, but there's no reason to do two separate with statements.

with open(path_1, 'a') as file_1, open(path_2, 'r') as file_2:
    for line in file_2:
        if 'tests/file/myword' in line:
            file_1.write(line)

Safe and memory-saving:

with open("out1.txt", "w") as fw, open("in.txt","r") as fr: 
    fw.writelines(l for l in fr if "tests/file/myword" in l)

It doesn't create temporary lists (what readline and [] would do, which is a non-starter if the file is huge), all is done with generator comprehensions, and using with blocks ensure that the files are closed on exit.

f = open('list1.txt')
f1 = open('output.txt', 'a')

# doIHaveToCopyTheLine=False

for line in f.readlines():
    if 'tests/file/myword' in line:
        f1.write(line)

f1.close()
f.close()

Now Your code will work. Try This one.

readlines() reads the entire input file into a list and is not a good performer. Just iterate through the lines in the file. I used 'with' on output.txt so that it is automatically closed when done. That's not needed on 'list1.txt' because it will be closed when the for loop ends.

#!/usr/bin/env python
with open('output.txt', 'a') as f1:
    for line in open('list1.txt'):
        if 'tests/file/myword' in line:
            f1.write(line)