python 中的文件“~”分隔文件中的问题

Question

I am a newbie in Python. i have "~" separeted file in a folder for eg.

2021-11-02 23:04:17.106
#$!pre-dump!$#00067evnISO-8859-1    
#$!languages!$#
##$!cdf!$#
UAFR~UAFRICA~
UEUE~UEUR (CIS + TURKEY)~
UEUW~UEUR (WESTERN)~
UFEA~UASIA~
UGBR~UUNITED KINGDOM~
ULAM~ULATIN AMERICA~
UMEA~UMIDDLE EAST~
UNAM~UNORTH AMERICA~
UOCE~UOCEANIA~
UUSA~UUSA~

the files may have lines without "~". i need to get the lines which has "~" in a text file and here is the python script which i've done

import os
sourcepath = os.listdir('input/')
for file in sourcepath:
    input_file = 'input/' + file
    print('conversion is going for:' + input_file)
    with open(input_file, 'r+', encoding='cp437') as input_file:
        input_file.seek(0)
        lines = input_file.readlines()
        input_file.seek(0)
        for line in lines:
            if "~" in line:
                input_file.write(line)

and below is the input file screenshot input file screenshot and here is the output which i got after running the above python script output of the python script and i really don't know where i am going wrong... please help me..

Answer 1

Rewriting a file in place doesn't delete extraneous data if you write less new data than the original file size. But it's a trivial fix; just explicitly truncate the file after you rewrite it, eg:

import os

for file in os.listdir('input/'):
    input_file = 'input/' + file
    print('conversion is going for:' + input_file)
    with open(input_file, 'r+', encoding='cp437') as input_file:
        # Removed unnecessary initial seek; r+ defaults to beginning of file
        lines = input_file.readlines()
        input_file.seek(0)
        for line in lines:
            if "~" in line:
                input_file.write(line)
        input_file.truncate()  # With no arguments, truncate truncates to current file offset

Optionally, the truncate can be done after the .seek(0) instead, which empties the file before rewriting any of it (at the risk of losing all your data if something goes wrong writing out the new data, and possibly causing the new file to use new disk sectors instead of reusing already allocated space).