从一个文件读取并在Python中写入另一个文件

Question

I'm writing a program that finds certain lines of text in a file and writes them to another file to get rid of all the annoying text in between (it's a .vmg file). Through my skills of python and googleing I have writen the following program.

with open("filein.txt") as f:
    with open("fileout.txt", "w") as f1:
        for line in f:
            if "telephone number" in line:
                f1.write(line)
            if "telephone number" and "X-BOX" in line:
                f1.write(line)
            if "Subject" in line:
                f1.write(line)

The program is working fine, but for the "subject" I want to tell the program to write not just the single line of text where the keyword "subject" is, but until it reaches a certain keyword (in my case that is "END:VBODY"). What should I do?

Answer 1

Not the most elegant, but you can just use a flag to indicate whether or not the cursor is in between the Subject and END:VBODY::

with open("filein.txt") as f:
    with open("fileout.txt", "w") as f1:
        for line in f:
            if in_subject:
                f1.write(line)
                if "END:VBODY" in line:
                    in_subject = False
            else:
                if "telephone number" in line:
                    f1.write(line)
                if "telephone number" and "X-BOX" in line:
                    f1.write(line)
                if "Subject" in line:
                    in_subject = True
                    f1.write(line)

Answer 2

If you just need this one particular case, you can walk away with simple state variable. Something like this:

inside_subject = False
with open("fileout.txt", "w") as out:
    for line in open("filein.txt", "r"):
        if inside_subject:
            if not "END:VBODY" in line:
                print line
            else:
                inside_subject = False
        else:
            if "telephone number" in line:
                out.write(line)
            elif "telephone number" in line and "X-BOX" in line: # will never match this though
                out.write(line)
            elif "Subject" in line:
                out.write(line)
                inside_subject = True

Though if you'll have more conditions, consider using some state machine.

Answer 3

if "Subject" in line:
    f1.write(line[:line.index("END:VBODY")])

Answer 4

Here is another working solution just by adding a while loop under the if "Subject" in line condition.

with open("filein.txt") as f:
    with open("fileout.txt", "w") as f1:
        for line in f:
            if "telephone number" in line:
                f1.write(line)
            if "telephone number" and "X-BOX" in line:
                f1.write(line)
            if "Subject" in line:
                f1.write(line)

                # new code added here
                while 'END:VBODY' not in line:
                    line = f.next()
                    f1.write(line)