Python Print To Standard Error
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Print Sys.stderr Comments In Python
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Python Redirect Stderr
can I redirect the output of print function to stderr? up vote 5 down vote favorite 1 There're lots of print function (python 2.7) in my program. Is there any way I can add a few lines then all the output can be redirected to stderr? What I want is python codes but not linux pipeline. For example, my program is like: print 'hello standard error stream function in python world' I would like to add some codes like: redirect_output_to_stderr() print 'hello world' Then all the output can be redirected to stderr. I know print >> sys.stderr, 'hello world' can achieve my goal, but is it any way that can prevent from modifying the existed codes? python python-2.7 stderr share|improve this question edited Apr 7 '13 at 8:32 Ikke 51k167096 asked Apr 7 '13 at 8:25 waitingkuo 15.4k75780 1 The only way to do that without modifying the code is to use a shell's redirection commands. –Roland Smith Apr 7 '13 at 8:42 Oh, I guess what I need is preventing from modified the existed print functions. Thank you for mentioned that :) –waitingkuo Apr 7 '13 at 8:45 add a comment| 3 Answers 3 active oldest votes up vote 8 down vote accepted Do this in your method: import sys sys.stdout = sys.stderr share|improve this answer answered Apr 7 '13 at 8:31 MostafaR 2,166621 add a comment| up vote 6 down vote In python 2.7 you can do: import sys print >> sys.stderr, "To stderr." Or you can import the behavior from 3.x: from __future__ import print_fun
concept of standard input, standard output, and standard error. This section is for the rest of you. Standard output and standard error (commonly abbreviated stdout and stderr) are pipes that are built into every UNIX system. When lambda cannot have return statement you print something, it goes to the stdout pipe; when your program crashes and file=sys.stderr invalid syntax prints out debugging information (like a traceback in Python), it goes to the stderr pipe. Both of these pipes are ordinarily print( hello world end= o ) in python just connected to the terminal window where you are working, so when a program prints, you see the output, and when a program crashes, you see the debugging information. (If you're working on a system with http://stackoverflow.com/questions/15860372/in-python-can-i-redirect-the-output-of-print-function-to-stderr a window-based Python IDE, stdout and stderr default to your "Interactive Window".) Example10.8.Introducing stdout and stderr >>> for i in range(3): ... print 'Dive in' Dive in Dive in Dive in >>> import sys >>> for i in range(3): ... sys.stdout.write('Dive in') Dive inDive inDive in >>> for i in range(3): ... sys.stderr.write('Dive in') Dive inDive inDive in As you saw in Example6.9, "Simple Counters", you can use Python's built-in range function http://www.diveintopython.net/scripts_and_streams/stdin_stdout_stderr.html to build simple counter loops that repeat something a set number of times. stdout is a file-like object; calling its write function will print out whatever string you give it. In fact, this is what the print function really does; it adds a carriage return to the end of the string you're printing, and calls sys.stdout.write. In the simplest case, stdout and stderr send their output to the same place: the Python IDE (if you're in one), or the terminal (if you're running Python from the command line). Like stdout, stderr does not add carriage returns for you; if you want them, add them yourself. stdout and stderr are both file-like objects, like the ones you discussed in Section10.1, "Abstracting input sources", but they are both write-only. They have no read method, only write. Still, they are file-like objects, and you can assign any other file- or file-like object to them to redirect their output. Example10.9.Redirecting output [you@localhost kgp]$ python stdout.py Dive in [you@localhost kgp]$ cat out.log This message will be logged instead of displayed(On Windows, you can use type instead of cat to display the contents of a file.) If you have not already done so, you can download this and other examples used in this book. #stdout.py import sys print 'D
Post #1 of 2 (23257 views) Permalink Simple print to stderr By default the print statement sends to stdout I want to send to http://www.gossamer-threads.com/lists/python/python/689509 stderr Try print "my meeage", file=sys.stderr I got > SyntaxError: invalid syntax I http://www.python-course.eu/python3_print.php try print "my message", sys.stderr But it still sent to stdout. What is the syntax? I wouldn't understand Python's manual > print([object, ...][, sep=' '][, end='n'][, file=sys.stdout])¶ > > Print object(s) to the stream file, separated by sep and followed by end. sep, end and file, if present, must be in python given as keyword arguments. > > All non-keyword arguments are converted to strings like str() does and written to the stream, separated by sep and followed by end. Both sep and end must be strings; they can also be None, which means to use the default values. If no object is given, print() will just write end. > > The file argument must print sys.stderr comments be an object with a write(string) method; if it is not present or None, sys.stdout will be used. -- http://mail.python.org/mailman/listinfo/python-list mnordhoff at mattnordhoff Oct27,2008,11:41AM Post #2 of 2 (22979 views) Permalink Re: Simple print to stderr [In reply to] RC wrote: > By default the print statement sends to stdout > I want to send to stderr > > Try > > print "my meeage", file=sys.stderr > > I got >> SyntaxError: invalid syntax > > I try > > print "my message", sys.stderr > > But it still sent to stdout. > What is the syntax? > > I wouldn't understand Python's manual
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