Writing to a file in a for loop

Question

text file   open  new txt    r    lines   text file readlines    for line in lines          var1  var2   line split               myfile   open  xyz txt    w           myfile writelines var1          myfile close   text file close     I have 10 lines of text in new txt like Adam 8154 George 5234 and so on  Now i want a text file which contains only the names  xyz txt must contain Adam George and so on  Now the above code leaves me with the 10th name only    How to have all the 10 names in a single text file

User · Answer

It s preferable to use context managers to close the files automatically  with open  new txt    r    open  xyz txt    w   as textfile  myfile      for line in textfile          var1  var2   line split               myfile writelines var1

User · Answer

The main problem was that you were opening closing files repeatedly inside your loop   Try this approach   with open  new txt   as text file  open  xyz txt    w   as myfile        for line in text file          var1  var2   line split               myfile write var1   n     We open both files at once and because we are using with they will be automatically closed when we are done  or an exception occurs   Previously your output file  was repeatedly openend inside your loop   We are also processing the file line-by-line  rather than reading all of it into memory at once  which can be a problem when you deal with really big files    Note that write   doesn t append a newline    n   so you ll have to do that yourself if you need it  I replaced your writelines   with write   as you are writing a single item  not a list of items    When opening a file for rread  the  r  is optional since it s the default mode

User · Answer

That is because you are opening   writing and closing the file 10 times inside your for loop  myfile   open  xyz txt    w   myfile writelines var1  myfile close     You should open and close your file outside for loop   myfile   open  xyz txt    w   for line in lines      var1  var2   line split           myfile write   s n    var1   myfile close   text file close     You should also notice to use write and not writelines    writelines writes a list of lines to your file   Also you should check out the answers posted by folks here that uses with statement  That is the elegant way to do file read write operations in Python

[python] Writing to a file in a for loop

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