如何将输出写入文件python

Question

so I have the file: data2.txt

Lollypop,
Lolly pop,
ooh 
lolly,
lolly, lolly;
lollypop, lollypop,
ooh lolly, lolly, lolly,
lollypop!
ba dum dum dum ...

LOL :-)

i need to loop through each line of data2.txt printing only lines that contain the string 'lol' and print the output to a newfile

with open("data3.txt") as g:
    with open("data2.txt") as lfp:
        for lin in lfp:
            if 'lol' in lin:
                g.write(str(lin))
            elif 'LOL' in lin:
                g.write(str(lin))
            elif 'Lol' in lin:
                g.write(str(lin))

But I keep getting error:

    g.write(str(lin))
io.UnsupportedOperation: not writable

Answer 1

You need to open with w for writing:

with open("data3.txt","w") as g:
    with open("data2.txt") as lfp:

You can also simplify to:

with open("data3.txt", "w") as g, open("data2.txt") as lfp:
        for lin in lfp:
            if 'lol' in lin.lower():
                g.write(lin)

Or use writelines:

with open("data3.txt", "w") as g, open("data2.txt") as lfp:
        g.writelines(line for line in lfp if "lol" in line.lower())

line is already a string so you don't need to call str on it, using "lol" in line.lower() will match all you cases.

If you were explicitly looking for "lol", "Lol", "LOL" , any would be a nicer approach.

with open("data3.txt", "w") as g, open("data2.txt") as lfp:
    poss = ("lol", "Lol", "LOL")
    g.writelines(line for line in lfp 
                    if any(s in line for s in poss))

All the modes are explained in the docs

Answer 2

The problem is in the line with open("data3.txt") as g:

You didn't provide open with a mode, and the default is r which is only for reading. Use with open("data3.txt", 'w') as g: if you want to replace the file if it is already exists or with open("data3.txt", 'a') as g: if you want to append to the file if it is already exists.