Python 3: Write to stdout and stderr

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Writing to Standard Output (stdout) using print is simple:

print( "Hello Standard Output!" )

print( "Hello Standard Output!" )

But if you want to write to Standard Error (stderr), you'll have to import the sys library:

import sys

print( "Hello Standard Error!", file=sys.stderr )

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import sys

print( "Hello Standard Error!", file=sys.stderr )

You can also write to stdout or stderr using the sys.stdout and sys.stderr file objects:

import sys

sys.stdout.write( "Hello Standard Output!\n" )
sys.stderr.write( "Hello Standard Error!\n" )

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import sys

sys.stdout.write( "Hello Standard Output!\n" )
sys.stderr.write( "Hello Standard Error!\n" )

Whereas print automatically adds a newline character \n at the end, with sys.stdout.write and sys.stderr.write, you need to explicitly add it.

• sys — System-specific parameters and functions — Python 3 documentation

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