Help saving output onto a text file

[Scott David Daniels]

continium at gmail.com wrote:
> If I have a simple program that for example calculates
> the squares of 2 to 100 times, how can I write the resulting output
> onto a separate text file?
> 
> I know about the open() function and I can write strings and such in
> text files but I'm not able to write the output of my programs.

Simplest way:

     results = open('myname.txt', 'w')
     print >>results, 'This goes out.'
     print >>results, 'Similarly, this is the next line.'
     results.close()

Slightly more obscure, but if your program is already printing:

     import sys
     former, sys.stdout = sys.stdout, open('myname.txt', 'w')
     <do anything that prints here>
     results, sys.stdout = sys.stdout, former
     results.close()

Really the closes (and swap back in the change-stdio case) should be done
in a "finally clause of a try: ... finally: ... block, but that may
not be where you are now.

So I'd really use (for myself):

Explicit file prints:
     results = open('myname.txt', 'w')
     try:
         print >>results, 'This goes out.'
         print >>results, 'Similarly, this is the next line.'
         # You can call functions to print, but they need to get
         # results and use the same form as above.
         # If you write your code using print >>var, ...
         # you can set var to None to go to the "normal" output.
     finally:
         results.close()

Captured "standard" output:
     import sys
     former, sys.stdout = sys.stdout, open('myname.txt', 'w')
     try:
         print 'This goes out.'
         print 'Similarly, this is the next line.'
         # Even if you call a function that prints here,
         # its output is captured to your file
     finally:
         results, sys.stdout = sys.stdout, former
         results.close()

--Scott David Daniels
scott.daniels at acm.org