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I'm writing a backup script I intend to execute in a cronjob every night.
The script sets sys.stdout and sys.stderr to an output file to keep a log of what happens.
To do the backup I use the following code
cmd = 'rsync -av --del --stats --filter "- .thumbnails/" ' + \
'--filter "- *~" --filter "- *.iso" --filter "- lost+found/" ' + \
'--filter "- .cache/" --filter "- tmp/" --filter "- *.mp3" ' + \
'--filter "- *.log" ' + srcDir + ' ' + dstDir
print "Executing '"+cmd+"' ..."
try:
sys.stdout.flush()
sys.stderr.flush()
retcode = subprocess.call( cmd, stdin = sys.stdin, stdout = sys.stdout,
stderr=sys.stderr, shell=False )
if retcode < 0:
print >>sys.stderr, "Command was terminated by signal", -retcode
elif retcode > 0:
print >>sys.stderr, "Command returned code ", retcode
except OSError, e:
print >>sys.stderr, "Execution failed:", e
I add print statements before and after the subprocess call. The problem is that I get the output of the subprocess call before any output of my print instructions before the call. I added the flush() calls but it has no effect.
Why is this happening and how could I change this behaviour ?
998
Redirecting stdout and stderr to a file: The I/O streams can be redirected by putting the n> operator in use, where n is the file descriptor number. For redirecting stdout, we use “1>” and for stderr, “2>” is added as an operator.
To capture stdout output from a Python function call, we can use the redirect_stdout function. to call redirect_stdout with the f StringIO object. Then we call do_something which prints stuff to stdout. And then we get the value printed to stdout with f.
A built-in file object that is analogous to the interpreter's standard output stream in Python. stdout is used to display output directly to the screen console. Output can be of any form, it can be output from a print statement, an expression statement, and even a prompt direct for input.
To write to a text file in Python, you follow these steps: First, open the text file for writing (or append) using the open() function. Second, write to the text file using the write() or writelines() method. Third, close the file using the close() method.
I just found the solution here in a Stackoverflow answer.
Replace
sys.stderr = sys.stdout = logFile = open( tmpLogFileName, 'a' )
with
sys.stderr = sys.stdout = logFile = open( tmpLogFileName, 'a', 0 )
This tells python to not assign any output buffer to file.
87
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