python sys.exit not working in try
Question:
Python 2.7.5 (default, Feb 26 2014, 13:43:17)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> try:
... sys.exit()
... except:
... print "in except"
...
in except
>>> try:
... sys.exit(0)
... except:
... print "in except"
...
in except
>>> try:
... sys.exit(1)
... except:
... print "in except"
...
in except
Why am not able to trigger sys.exit() in try, any suggestions…!!!
The code posted here has all the version details.
I have tried all possible ways i know to trigger it, but i failed.
It gets to ‘except’ block.
Thanks in advance..
Answers:
sys.exit()
raises an exception, namely SystemExit
. That’s why you land in the except
-block.
See this example:
import sys
try:
sys.exit()
except:
print(sys.exc_info()[0])
This gives you:
<type 'exceptions.SystemExit'>
Although I can’t imagine that one has any practical reason to do so, you can use this construct:
import sys
try:
sys.exit() # this always raises SystemExit
except SystemExit:
print("sys.exit() worked as expected")
except:
print("Something went horribly wrong") # some other exception got raised
based on python wiki :
Since exit() ultimately “only” raises an exception, it will only exit the process when called from the main thread, and the exception is not intercepted.
And:
The exit
function is not called when the program is killed by a signal, when a Python fatal internal error is detected, or when os._exit()
is called.
Therefore, If you use sys.exit()
within a try
block python after raising the SystemExit
exception python refuses of completing the exits
‘s functionality and executes the exception
block.
Now, from a programming perspective you basically don’t need to put something that you know definitely raises an exception in a try
block. Instead you can either raise a SystemExit
exception manually or as a more Pythonic approach if you don’t want to loose the respective functionalities of sys.exit()
like passing optional argument to its constructor you can call sys.exit()
in a finally
, else
or even except
block.
Method 1 (not recommended)
try:
# do stuff
except some_particular_exception:
# handle this exception and then if you want
# do raise SystemExit
else:
# do stuff and/or do raise SystemExit
finally:
# do stuff and/or do raise SystemExit
Method 2 (Recommended):
try:
# do stuff
except some_particular_exception:
# handle this exception and then if you want
# do sys.exit(stat_code)
else:
# do stuff and/or do sys.exit(stat_code)
finally:
# do stuff and/or do sys.exit(stat_code)
Python 2.7.5 (default, Feb 26 2014, 13:43:17)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> try:
... sys.exit()
... except:
... print "in except"
...
in except
>>> try:
... sys.exit(0)
... except:
... print "in except"
...
in except
>>> try:
... sys.exit(1)
... except:
... print "in except"
...
in except
Why am not able to trigger sys.exit() in try, any suggestions…!!!
The code posted here has all the version details.
I have tried all possible ways i know to trigger it, but i failed.
It gets to ‘except’ block.
Thanks in advance..
sys.exit()
raises an exception, namely SystemExit
. That’s why you land in the except
-block.
See this example:
import sys
try:
sys.exit()
except:
print(sys.exc_info()[0])
This gives you:
<type 'exceptions.SystemExit'>
Although I can’t imagine that one has any practical reason to do so, you can use this construct:
import sys
try:
sys.exit() # this always raises SystemExit
except SystemExit:
print("sys.exit() worked as expected")
except:
print("Something went horribly wrong") # some other exception got raised
based on python wiki :
Since exit() ultimately “only” raises an exception, it will only exit the process when called from the main thread, and the exception is not intercepted.
And:
The
exit
function is not called when the program is killed by a signal, when a Python fatal internal error is detected, or whenos._exit()
is called.
Therefore, If you use sys.exit()
within a try
block python after raising the SystemExit
exception python refuses of completing the exits
‘s functionality and executes the exception
block.
Now, from a programming perspective you basically don’t need to put something that you know definitely raises an exception in a try
block. Instead you can either raise a SystemExit
exception manually or as a more Pythonic approach if you don’t want to loose the respective functionalities of sys.exit()
like passing optional argument to its constructor you can call sys.exit()
in a finally
, else
or even except
block.
Method 1 (not recommended)
try:
# do stuff
except some_particular_exception:
# handle this exception and then if you want
# do raise SystemExit
else:
# do stuff and/or do raise SystemExit
finally:
# do stuff and/or do raise SystemExit
Method 2 (Recommended):
try:
# do stuff
except some_particular_exception:
# handle this exception and then if you want
# do sys.exit(stat_code)
else:
# do stuff and/or do sys.exit(stat_code)
finally:
# do stuff and/or do sys.exit(stat_code)