函数不写入文本文件

Question

I'm trying to make a sort of logbook in a text file to avoid re-doing efforts. I have the following function that perform this task:

def write_to_logbook(target_name):

   with open('C:\Documents\logbook.txt', 'a+') as f:
      for lines in f:
          if target_name not in lines:
              f.write(target_name + '\n')
              f.close() #when I didn't have f.close() here, it also wasn't writing to the txt file

When I check the text file after I run the script, it remains empty. I'm not sure why.

I call it as such (in reality target name is pulled down from a unique ID, but since I don't want to put everything here, this is the gist):

target_name = 'abc123'
write_to_logbook(target_name)

Answer 1

You need to (potentially) read the entire file before you can decide if target_name has to be added to the file.

def write_to_logbook(target_name):
    fname = r'C:\Documents\logbook.txt')

    with open(fname) as f:
        if any(target_name in line for line in f):
            return

    with open(fname, 'a') as f:
        print(target_name, file=f)

any will return True as soon as any line containing target_name is found, at which point the function itself will return.

If the target name isn't found after reading the entire file, then the second with statement will append the target name to the file.

Answer 2

I got it sorted.I used chepner's solution as a jumping off point, since it didn't exactly work (only wrote one target_name for some reason) and kind of did a hybrid of the two:

def write_to_logbook(target_name):
    fname = 'filepath'

    with open(fname) as f:
        for lines in f:
            if target_name in lines:
                return

    with open(fname, 'a+') as f:
        f.write(target_name + '\n')

Thanks for the solution, it helped.