Here is code from a tutorial in A Byte of Python:
import sys
filename = 'poem.txt'
def readfile(filename):
#Print a file to standard output
f = file(filename)
while True:
line = f.readline()
if len(line) == 0:
break
print line,
f.close()
if len(sys.argv) < 2:
print 'No action specified'
sys.exit() //<--This is where the error is occurring
if sys.argv[1].startswith('--'):
option = sys.argv[1][2:] #fetches sys.argv[1] without first 2 char
if option == 'version':
print 'Version 1.2'
elif option == 'help':
print '''\
This program prints files to the standard output.
Any number of files can be specified.
Options include:
--version: Prints the version number
--help: Displays this help'''
else:
print 'Unknown option'
sys.exit()
else:
for filename in sys.argv[1:]:
readfile(filename)
When I run this code, this is the error that appears:
Traceback (most recent call last):
File "C:/Python/sysmodulepr.py", line 17, in <module>
sys.exit()
SystemExit
I don't understand why. Please help.
It's telling you that sys.exit() has executed on line 17 of your program.
The entry for for sys.exit in the Python documentation tells you that this exits your program.
There's no way this line can execute without producing other output, so I think there's something missing in the question.
If you're using IDLE, it will print the stack anyway. Try running your script from the command line, it won't print that error message when executed outside the IDE.
It's not an error. sys.exit() raises SystemExit exception to allow try:... finally block to cleanup used resources
Try in Idle:
import sys
sys.exit()
From documentation for sys.exit():
Exit from Python. This is implemented by raising the SystemExit exception, so cleanup actions specified by finally clauses of try statements are honored, and it is possible to intercept the exit attempt at an outer level.
edit
The error shouldn't be normally printed unless you're trying to run the script in some interactive interpreters (for example Idle).
It's nothing to worry about, but the script looks like it's standalone, so you should use it as such.
Related
I need to call 1 script(test.py) every 5 minutes, so i have used another script timer.py with following code:
import time
while(1==1):
execfile("test.py")
time.sleep(300)
This works correctly.
But it stopped working after few iterations. After debugging i found that there is a flow in test.py which uses following code:
sys.exit()
So, this is causing both test.py and timer.py to stop.
what changes should be done, so as to continue timer.py since i want sys.exit() to only exit test.py and not timer.py
sys.exit() doesn't do more then raising SystemExit (a BaseException subclass), which can be caught like any exception e.g:
import time
while True:
try:
execfile("test.py")
except SystemExit:
print("ignoring SystemExit")
finally:
time.sleep(300)
Use subprocess
import subprocess
import time
while(1==1):
subprocess.call(['python', './test.py'])
time.sleep(300)
You could even remove the python word if the test.py file has a shebang comment on the first line:
#!/usr/bin/env python
This is not exactly the same, as it will start a new interpreter, but the results will be similar.
You should be able to use:
try:
# Your call here
except BaseException as ex:
print("This should be a possible sys.exit()")
Check out the documentation for more information.
Try this:
import time
import os
while True:
os.system("python test.py") # if you are not running script from same directory then mention complete path to the file
time.sleep(300)
I'm creating a program and I recently started exception handling. The program worked fine a couple times but now I'm getting an IndentationError every time it starts, which is bizarre because it worked fine before. It is large, so I'm only including a snippet of the program. Let me know if you need the whole thing.
The only way I can get it to work is if I delete the command
I've included some lines in-between the commands so you can more clearly identify them. The problem command is the one in the middle.
elif 'python' in cmd:
pythonProgram = cmd.split(' ')[1]
execfile(pythonProgram)
elif 'cd' in cmd:
desired_directory = cmd.split(' ')[1]
if desired_directory == "..":
os.chdir('..')
else:
try:
os.chdir(desired_directory)
print "'%s' Is not a valid directory!" % desired_directory
elif 'ver' in cmd:
print"JDOS_2", currentVersion
I've also attempted to hash out the lower elif and gotten the same error with the next elif statement in the program.
This seems like a simple problem, and I'm most likely overseeing something, but the indentations of elif commands are the same. This is the error output.
File "/Users/#######/PycharmProjects/untitled/JDOS/SYS64/jdosos.py", line 64
elif cmd == "ver":
^
IndentationError: unexpected unindent
Process finished with exit code 0
And I haven't had any problems mixing spaces and indents as its littered all over my program.
A bit late, but I needed a matching except block to go with the try argument.
This is the fixed code and works perfectly.
elif 'cd' in cmd:
desired_directory = cmd.split('cd ')[1]
if desired_directory == "..":
os.chdir('..')
else:
try:
os.chdir(desired_directory)
except OSError as e:
print("'%s' Is not a valid directory!" % desired_directory)
I have pexpect working, but I am having problems printing the output back from it. In my test script below, it creates the ssh connection, and then sends a sudo su -, then my password, and then sends a line that would require sudo access to do (I have also added p.interact() a few times to make sure it is at root). The problem I am having, is with returning the output of the commands I run. In the end I am wanting to run some top commands, and some du -h, and other(much more complex) space commands. But currently when it tries to print p.before, I get:
Traceback (most recent call last):
File "./ssh.py", line 37, in <module>
print p.before()
TypeError: 'str' object is not callable
Here is the script I am working from(edited to remove my pass and such)
#!/usr/bin/env python
import pexpect
import struct, fcntl, os, sys, signal
def sigwinch_passthrough (sig, data):
# Check for buggy platforms (see pexpect.setwinsize()).
if 'TIOCGWINSZ' in dir(termios):
TIOCGWINSZ = termios.TIOCGWINSZ
else:
TIOCGWINSZ = 1074295912 # assume
s = struct.pack ("HHHH", 0, 0, 0, 0)
a = struct.unpack ('HHHH', fcntl.ioctl(sys.stdout.fileno(), TIOCGWINSZ , s))
global global_pexpect_instance
global_pexpect_instance.setwinsize(a[0],a[1])
ssh_newkey = 'Are you sure you want to continue connecting'
p=pexpect.spawn('ssh user#localhost')
i=p.expect([ssh_newkey,'password:',pexpect.EOF,pexpect.TIMEOUT],1)
if i==0:
print "I say yes"
p.sendline('yes')
i=p.expect([ssh_newkey,'password:',pexpect.EOF])
if i==1:
print "I give password",
p.sendline("mypassword")
elif i==2:
print "I either got key or connection timeout"
pass
elif i==3: #timeout
pass
global global_pexpect_instance
global_pexpect_instance = p
p.sendline("sudo su -")
p.sendline("mypasswd")
p.sendline("mkdir /home/user/test")
print p.before
I am working off of this link: http://linux.byexamples.com/archives/346/python-how-to-access-ssh-with-pexpect/
Any help is much appreciated.
EDIT: As Armin Rigo pointed out below. I was calling to p.before as a function like p.before(). Stupid mistake on my part, as this explains why I was getting this error today, and not yesterday when I was trying this. After making that change to my script, and modifying the command being sent, print p.before, and no output is returned. Any other ways to return output from a sendline() command?
Use logfile, that logfile is store all output in terminal.use that example code:-
child = pexpect.spawn("ssh user#localhost")
child.logfile = open("/tmp/mylog", "w")
child.expect(".*assword:")
child.send("guest\r")
child.expect(".*\$ ")
child.sendline("python -V\r")
open the log file and see everything in terminals event
To fetch the complete output after sendline use child.read()
e.g.
cmd_resp = pexpect.spawnu(cmd) # for execution of the command
str_to_search = 'Please Enter The Password'
cmd_resp.sendline('yes') # for sending the input 'yes'
resp = cmd_resp.expect([str_to_search, 'password:', EOF], timeout=30) # fetch the output status
if resp == 1:
cmd_resp.sendline(password)
resp = cmd_resp.expect([str_to_search, 'outputString:', EOF], timeout=30)
print(cmd_resp.read()) # to fetch the complete output log
p.before is a string - not a function. To see the output you have to write
print p.before.
Hope this might help you
I need a method to run a python script file, and if the script fails with an unhandled exception python should exit with a non-zero exit code. My first try was something like this:
import sys
if __name__ == '__main__':
try:
import <unknown script>
except:
sys.exit(-1)
But it breaks a lot of scripts, due to the __main__ guard often used. Any suggestions for how to do this properly?
Python already does what you're asking:
$ python -c "raise RuntimeError()"
Traceback (most recent call last):
File "<string>", line 1, in <module>
RuntimeError
$ echo $?
1
After some edits from the OP, perhaps you want:
import subprocess
proc = subprocess.Popen(['/usr/bin/python', 'script-name'])
proc.communicate()
if proc.returncode != 0:
# Run failure code
else:
# Run happy code.
Correct me if I am confused here.
if you want to run a script within a script then import isn't the way; you could use exec if you only care about catching exceptions:
namespace = {}
f = open("script.py", "r")
code = f.read()
try:
exec code in namespace
except Exception:
print "bad code"
you can also compile the code first with
compile(code,'<string>','exec')
if you are planning to execute the script more than once and exec the result in the namespace
or use subprocess as described above, if you need to grab the output generated by your script.
I have seen several questions about exiting a script after a task is successfully completed, but is there a way to do the same for a script which has failed? I am writing a testing script which just checks that a camera is functioning correctly. If the first test fails it is more than likely that the following tests will also fail; therefore, I want the first failure to invoke an exit and provide output to screen letting me know that there was an error.
I hope this is enough information; let me know if more details are required to help me.
Are you just looking for the exit() function?
import sys
if 1 < 0:
print >> sys.stderr, "Something is seriously wrong."
sys.exit(1)
The (optional) parameter of exit() is the return code the script will return to the shell. Usually values different than 0 signal an error.
You can use sys.exit() to exit. However, if any code higher up catches the SystemExit exception, it won't exit.
You can raise exceptions to identify error conditions. Your top-level code can catch those exceptions and handle them appropriately. You can use sys.exit to exit. E.g., in Python 2.x:
import sys
class CameraInitializationError(StandardError):
pass
def camera_test_1():
pass
def camera_test_2():
raise CameraInitializationError('Failed to initialize camera')
if __name__ == '__main__':
try:
camera_test_1()
camera_test_2()
print 'Camera successfully initialized'
except CameraInitializationError, e:
print >>sys.stderr, 'ERROR: %s' % e
sys.exit(1)
You want to check the return code from the c++ program you are running, and exit if it indicates failure. In the code below, /bin/false and /bin/true are programs that exit with error and success codes, respectively. Replace them with your own program.
import os
import sys
status = os.system('/bin/true')
if status != 0:
# Failure occurred, exit.
print 'true returned error'
sys.exit(1)
status = os.system('/bin/false')
if status != 0:
# Failure occurred, exit.
print 'false returned error'
sys.exit(1)
This assumes that the program you're running exits with zero on success, nonzero on failure.