What does "print >>" do in python?
Question:
I have to translate a code from python 2 into python 3 and I can’t understand what does print >>
do and how should I write it in python 3.
print >> sys.stderr, '--'
print >> sys.stderr, 'entrada1: ', entrada1
print >> sys.stderr, 'entrada2: ', entrada2
print >> sys.stderr, '--'
Answers:
The >> sys.stderr
part makes the print
statement output to stderr instead of stdout in Python 2.
To quote the documentation:
print
also has an extended form, defined by the second portion of the
syntax described above. This form is sometimes referred to as “print
chevron.” In this form, the first expression after the >>
must
evaluate to a “file-like” object, specifically an object that has a
write()
method as described above. With this extended form, the
subsequent expressions are printed to this file object. If the first
expression evaluates to None
, then sys.stdout
is used as the file for
output.
In Python 3 use the file
argument to the print()
function:
print("spam", file=sys.stderr)
To convert these from Python 2 to Python 3, change:
print >>sys.stderr, 'Hello'
to:
print('Hello', file=sys.stderr)
For printing to stderr
note
sys.stderr.write()
is portable across versions, yet you need to add a newline, unlike print
; for instance
import sys
errlog = sys.stderr.write
errlog("an error messagen")
I have to translate a code from python 2 into python 3 and I can’t understand what does print >>
do and how should I write it in python 3.
print >> sys.stderr, '--'
print >> sys.stderr, 'entrada1: ', entrada1
print >> sys.stderr, 'entrada2: ', entrada2
print >> sys.stderr, '--'
The >> sys.stderr
part makes the print
statement output to stderr instead of stdout in Python 2.
To quote the documentation:
syntax described above. This form is sometimes referred to as “print
chevron.” In this form, the first expression after the>>
must
evaluate to a “file-like” object, specifically an object that has a
write()
method as described above. With this extended form, the
subsequent expressions are printed to this file object. If the first
expression evaluates toNone
, thensys.stdout
is used as the file for
output.
In Python 3 use the file
argument to the print()
function:
print("spam", file=sys.stderr)
To convert these from Python 2 to Python 3, change:
print >>sys.stderr, 'Hello'
to:
print('Hello', file=sys.stderr)
For printing to stderr
note
sys.stderr.write()
is portable across versions, yet you need to add a newline, unlike print
; for instance
import sys
errlog = sys.stderr.write
errlog("an error messagen")