Stdout issue in python

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December 31st, 2012, 01:17 AM

Sachin Bali

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Stdout issue in python

Hi,

I am working on a script. Requirement is to divert all output to a file. I did this with below code-:

sys.stdout=open(output_file_name,'w')

Now, after execution of the script i want to print one line to console that, please check the output in "output_file_name".

But this line also get printed inside the file instead of console. Can any one help?

Regards,
Sachin Bali

December 31st, 2012, 01:38 AM

Scorpions4ever

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Back up the old sys.stdout into another variable before you make it write to a file:

Code:

old_stdout = sys.stdout
sys.stdout=open(output_file_name,'w')
# Do stuff here
old_stdout.write("Something that goes to the screen\n")

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December 31st, 2012, 02:15 AM

Sachin Bali

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Quote:

Originally Posted by Scorpions4ever

Back up the old sys.stdout into another variable before you make it write to a file:

Code:

old_stdout = sys.stdout
sys.stdout=open(output_file_name,'w')
# Do stuff here
old_stdout.write("Something that goes to the screen\n")

Yes,
it is working. Thanks.

But can you explain the reason why we need to store the sys.stdout to some other variable ?

Regards,
Sachin Bali

December 31st, 2012, 07:25 AM

Nyktos

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You can also use sys.__stdout__ which is supposed to contain the "original" value of sys.stdout as of the start of the program.

December 31st, 2012, 08:26 AM

b49P23TIvg

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>>> a = 43
>>> a = 'a string'
>>> # how will you recover 43?

In recent python2 there's some print syntax that directs output to some file not stdout.

In python3 print is a function that accepts a keyword file destination.

Code:

>>> help(print)
Help on built-in function print in module builtins:

print(...)
    print(value, ..., sep=' ', end='\n', file=sys.stdout)
    
    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file: a file-like object (stream); defaults to the current sys.stdout.
    sep:  string inserted between values, default a space.
    end:  string appended after the last value, default a newline.

Initially you might think as our group did that redirecting the print sink and input source are wonderful mechanisms for tests and whatnot. Later you'll realize that python has a wonderful StringIO class and that many functions are better off returning strings rather than directly printing them, and to separate opening files from using them. Instead of passing a file name argument pass open file-like objects.

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Stdout issue in python

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