Compare two different files line by line in python

Question

I have two different files and I want to compare theirs contents line by line  and write their common contents in a different file  Note that both of them contain some blank spaces   Here is my pseudo code   file1   open  some file 1 txt    r   file2   open  some file 2 txt    r   FO   open  some output file txt    w    for line1 in file1      for line2 in file2          if line1    line2              FO write   s n    line1    FO close   file1 close   file2 close     However  by doing this  I got lots of blank spaces in my FO file  Seems like common blank spaces are also written  I want to write only the text part  Can somebody please help me      For example  my first file  file1  contains data   Config  Hostname   TUVALU  BT  TS Ball Update Threshold   0 2  BT  TS Player Search Radius   4  BT  Ball Template Update   0   while second file  file2  contains data   Pole ID        2 Width          1280 Height         1024 Color Mode     0 Sensor Scale   1  Tracking ROI Size   4 Ball Template Update   0   If you notice  last two lines of each files are the same  hence  I want to write this file in my FO file  But  the problem with my approach is that  it writes the common blank space also  Should I use regex for this problem  I do not have experience with regex

User · Answer

Yet another example     from   future   import print function  Only for Python2  with open  file1 txt   as f1  open  file2 txt   as f2  open  outfile txt    w   as outfile      for line1  line2 in zip f1  f2           if line1    line2              print line1  end     file outfile    And if you want to eliminate common blank lines  just change the if statement to   if line1 strip   and line1    line2    strip   removes all leading and trailing whitespace  so if that s all that s on a line  it will become an empty string     which is considered false

User · Answer

Try this   from   future   import with statement  filename1    G   test1 TXT  filename2    G   test2 TXT    with open filename1  as f1     with open filename2  as f2        file1list   f1 read   splitlines         file2list   f2 read   splitlines         list1length   len file1list        list2length   len file2list        if list1length    list2length            for index in range len file1list                  if file1list index     file2list index                     print file1list index           file2list index                else                                      print file1list index           file2list index    Not-Equel        else            print  difference inthe size of the file and number of lines

User · Answer

This solution reads both files in one pass  excludes blank lines  and prints common lines regardless of their position in the file   with open  some file 1 txt    r   as file1      with open  some file 2 txt    r   as file2          same   set file1  intersection file2   same discard   n    with open  some output file txt    w   as file out      for line in same          file out write line

User · Answer

If order is preserved between files you might also prefer difflib  Although Rob  s result is the bona-fide standard for intersections you might actually be looking for a rough diff-like   from difflib import Differ  with open  cfg1 txt   as f1  open  cfg2 txt   as f2      differ   Differ        for line in differ compare f1 readlines    f2 readlines             if line startswith                   print line 2    end       That said  this has a different behaviour to what you asked for  order is important  even though in this instance the same output is produced

User · Answer

I have just been faced with the same challenge  but I thought  Why programming this in Python if you can solve it with a simple  grep    which led to the following Python code   import subprocess from subprocess import PIPE  try    output1  errors1   subprocess Popen   c   cygwin  bin  grep    -Fvf    c   file1 txt    c   file2 txt    shell True  stdout PIPE  stderr PIPE  communicate      output2  errors2   subprocess Popen   c   cygwin  bin  grep    -Fvf    c   file2 txt    c   file1 txt    shell True  stdout PIPE  stderr PIPE  communicate      if  len output1    len output2    len errors1    len errors2   gt  0       print   Compare result   There are differences         if  len output1    len output2   gt  0         print     Output differences             print  output1         print  output2       if  len errors1    len errors2   gt  0         print    Errors             print  errors1         print  errors2     else      print   Compare result   Both files are equal    except Exception as ex    print  Compare result   Exception during comparison      print ex     raise    The trick behind this is the following  grep -Fvf file1 txt file2 txt verifies if all entries in file2 txt are present in file1 txt  By doing this in both directions we can see if the content of both files are  equal   I put  equal  between quotes because duplicate lines are disregarded in this way of working   Obviously  this is just an example  you can replace grep by any commandline file comparison tool

User · Answer

Once the file object is iterated  it is exausted    gt  gt  gt  f   open  1 txt    w    gt  gt  gt  f write  1 n2 n3 n    gt  gt  gt  f close    gt  gt  gt  f   open  1 txt    r    gt  gt  gt  for line in f  print line     1  2  3    exausted  another iteration does not produce anything   gt  gt  gt  for line in f  print line      gt  gt  gt    Use file seek  or close open the file  to rewind the file    gt  gt  gt  f seek 0   gt  gt  gt  for line in f  print line     1  2  3

User · Answer

If you are specifically looking for getting the difference between two files  then this might help   with open  first file    r   as file1      with open  second file    r   as file2          difference   set file1  difference file2   difference discard   n    with open  diff txt    w   as file out      for line in difference          file out write line

[python] Compare two different files line by line in python

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