Copying from one text file to another using Python

Question

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

User · Answer

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

User · Answer

The oneliner   open  out1 txt    w   writelines  l for l in open  in txt   readlines   if  tests file myword  in l     Recommended with with   with open  in txt   as f      lines   f readlines       lines    l for l in lines if  ROW  in l      with open  out txt    w   as f1          f1 writelines lines    Using less memory   with open  in txt   as f      with open  out txt    w   as f1          for line in f              if  ROW  in line                  f1 write line

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

If all of that did not work try this  with open  quot hello txt quot   as f  with open  quot copy txt quot    quot w quot   as f1      for line in f          f1 write line

User · Answer

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

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

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