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

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

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

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

Examples related to python

Examples related to python-2.7