def main():
try:
print "hardfart"
return 0
except:
return 1
if __name__ == '__main__':
exit(main())
Can one kind programmer tell me why this spits out the following error on exit?
Traceback (most recent call last):
File "C:/Apps/exp_exit.py", line 9, in ,module.
exit(main())
File "C:\Apps\python2.7.2\lib\site.py", line 372 in __call__
raise SystemExit(code)
SystemExit: 0
This is causing an error on exit in a project that's set up similarly. For that project, after using gui2exe to compile an exe, when closing the program I get this related error:
Traceback (most recent call last):
File "checkHDBox.py", line 303, in <module>
NameError: name 'exit' is not defined
So if exit is generating this error, how do I exit then? And if I create an exception handler for exit, doesn't that replace the default action that python takes with the exit function?
Thanks.
Edit:
I think this answers my own question.
The traceback here is from IDLE, I think it's a default behavior from other sources I've read.
Traceback (most recent call last):
File "C:/Apps/exp_exit.py", line 9, in ,module.
exit(main())
File "C:\Apps\python2.7.2\lib\site.py", line 372 in __call__
raise SystemExit(code)
SystemExit: 0
The traceback here was fixed by using sys.exit() instead of exit(0)
Traceback (most recent call last):
File "checkHDBox.py", line 303, in <module>
NameError: name 'exit' is not defined
You exit a program by raising SystemExit. This is what exit() does. Someone has incorrectly written an exception handler that catches all exceptions. This is why you only catch the exceptions you can handle.
Related
I've been trying to get a specific (and most likely useless) effect on the traceback when I raise an error.
I would like to hide the raise Exception("Message") of the traceback inside my function and instead have my trace indicate the function call that triggered the raise inside the function
def crash(something):
if something > 200:
raise ValueError("Value too large !")
if __name__ == '__main__':
crash(500)
Normally generates :
Traceback (most recent call last):
File "file.py", line 7, in <module>
crash(500)
File "file.py", line 3, in crash
raise ValueError("Value too large !")
ValueError: Value too large !
Instead I would like to have this :
Traceback (most recent call last):
File "file.py", line 7, in <module>
crash(500)
ValueError: Value too large !
I find it clearer for the user trying to use the module because it clearly shows where the problem is as otherwise he could potentially think the module itself is at fault
I tried to find solution that would "remove" the last call from the traceback but it always had "side effects" like showing part of the code trying to remove the last trace call INSIDE the traceback itself, making it even more confusing. Sometimes it would also repeat the the traceback over what I really want.
For example using this :
def crash():
frame = sys._getframe(1)
tb = types.TracebackType(None, frame, frame.f_lasti, frame.f_lineno)
raise ValueError("Wrong value").with_traceback(tb)
Prints this :
Traceback (most recent call last):
File "file.py", line 34, in <module>
crash()
File "file.py", line 9, in crash
raise ValueError("Wrong value").with_traceback(tb)
File "file.py", line 34, in <module>
crash()
ValueError: Wrong value
I also tried using another function to create the trace myself but ended up with a weird behavior
def crash():
raise exception_no_raise(ValueError("Wrong value"))
def exception_no_raise(exc: Exception):
tb = None
depth = 0
while True:
try:
sys._getframe(depth)
depth += 1
except ValueError:
break
# for i in range(depth-1, 1, -1):
# frame = sys._getframe(i)
# tb = types.TracebackType(tb, frame, frame.f_lasti, frame.f_lineno)
# traceback.print_tb(tb)
# print(file=sys.stderr)
frame = sys._getframe(depth-1)
tb = types.TracebackType(tb, frame, frame.f_lasti, frame.f_lineno)
return exc.with_traceback(tb)
Prints :
Traceback (most recent call last):
File "file.py", line 32, in <module>
crash()
File "file.py", line 7, in crash
raise exception_no_raise(ValueError("Wrong value"))
File "file.py", line 32, in <module>
crash()
ValueError: Wrong value
Even tho when you use traceback.print_tb(tb) (before the return) you get the exact trace I want even tho using it to raise the exception doesn't print it :
File "file.py", line 34, in <module>
crash()
The last solution I found was to "strip" the last traceback from the tb.tb_next chain of traces after catching the exception and then re-raise it (but it showed the raise code anyway so ...)
I have difficulties to grasp how exactly traceback works and it seems that it changes drastically from version to version as I found code from Python 2 and 3 and also code the works in Python 3.8 and not before (related to the fact that you couldn't write to the tb.next of a trace before
Thanks for your help and clarifications !
I have python server that is massive and unexcepting turning it off, or interupting without saving data is bad idea.
I found sys.excepthook function and add it so there will be no way to acidently interupt program wih Ctrl+C, but
after first exception I use Ctrl+C or any other exepction it will like doesn't care about that and predent it doesn't
exists.
Code:
import time
import sys
def my_except_hook(exctype, value, traceback):
if exctype == KeyboardInterrupt:
print("WARNING: CTRL+C WAS PRESSED!")
main_loop()
else:
sys.__excepthook__(exctype, value, traceback)
def main_loop():
print("starting!")
while True:
print("tick")
time.sleep(1)
sys.excepthook = my_except_hook
main_loop()
Exception after second Ctrl+C:
Error in sys.excepthook:
Traceback (most recent call last):
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 8, in my_except_hook
main_loop()
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 17, in main_loop
time.sleep(1)
KeyboardInterrupt
Original exception was:
Traceback (most recent call last):
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 21, in <module>
main_loop()
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 17, in main_loop
time.sleep(1)
KeyboardInterrupt
Process finished with exit code -1073741510 (0xC000013A: interrupted by Ctrl+C)
Full output:
starting!
tick
tick
WARNING: CTRL+C WAS PRESSED!
starting!
tick
tick
Error in sys.excepthook:
Traceback (most recent call last):
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 8, in my_except_hook
main_loop()
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 17, in main_loop
time.sleep(1)
KeyboardInterrupt
Original exception was:
Traceback (most recent call last):
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 21, in <module>
main_loop()
File "C:\some\path\that\you\dont\have\to\known\except_test.py", line 17, in main_loop
time.sleep(1)
KeyboardInterrupt
Process finished with exit code -1073741510 (0xC000013A: interrupted by Ctrl+C)
I have the following function:
def findHardDriveLetter(drivename):
drives = win32api.GetLogicalDriveStrings()
drives = drives.split('\000')[:-1]
for drive in drives:
try:
volname = win32api.GetVolumeInformation(drive)[0].upper()
except:
pass
if volname == drivename.upper():
return drive
Depending on drive state, this error can occur, and I would like my except to catch the specific error:
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "<editor selection>", line 5, in findHardDriveLetter
error: (21, 'GetVolumeInformation', 'The device is not ready.')
Using type(exception).__name__, the error is reposted to be of type error. This seems to be different from the typical format of Python error types, and if I use
except error:
to catch it, I get this exception:
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "<editor selection>", line 20, in findHardDriveLetter
NameError: global name 'error' is not defined
So why is this not working as I expect, and how do I catch this exception without a generic except?
You can except win32api.error since this is the exception type you been getting, but it's generally used as the base class of all win32api exceptions...weird
try:
# ....
except win32api.error:
pass
I'm trying to make an automated test framework for a side-project and could use some help creating the assertion checks.
Running this in python...
assert(False)
Gives you this...
Traceback (most recent call last):
File "test.py", line 1, in <module>
assert(False)
AssertionError
As you can see the traceback lowest level is assert(False). So I made my custom assert that prints when the assert succeeds.
def custom_assert(condition):
if condition:
print("Yay! It werks!")
else:
raise Exception("Nay, it don't werks...")
custom_assert(False)
But instead of what assert gives, custom_assert gives me this.
Traceback (most recent call last):
File "test.py", line 14, in <module>
custom_assert(False)
File "test.py", line 12, in custom_assert
raise Exception("Nay, it don't werks...")
Exception: Nay, it don't werks...
Which is of course the default behavior. Perfectly useful 99.9999% of the time, but this is that one time it could be improved. It's not useful to know that the method I called to raise an error when the condition is false raised the error.
How can I make my custom_assert raise an exception with a traceback starting from the caller, the same way assert does?
P.S.: I don't want to print it, I want the exception to have properly modified traceback so it works properly with debuggers and other tools too!
Edit
To clarify, the traceback I want would be like this.
Traceback (most recent call last):
File "test.py", line 14, in <module>
custom_assert(False)
Exception: Nay, it don't werks...
Essentially what you want to do is something similar to this:
tb = None
try:
raise Exception('foo')
except Exception:
tb = sys.exc_info()[2]
tb.tb_frame = tb.tb_frame.f_back # This line doesn't work
raise Exception('Nay it doesnt werks').with_traceback(tb)
but you can't assign tb_frame, and from mucking around in the CPython code, this is C-generated data structures (not python) (see sys._getframe())
So your only option left is to mock the entire machinery and then convince python to use your stack. This looks like what jinja2 is doing. If that's what you choose to do, good luck! (It's out of my scope at that point)
I have a traceback print and want to customize the last part of it.
What: The error occurred in another process and traceback lies there (as is the case in multiprocessing).
Problem: I want to have the full traceback and error report.
Similar to this code:
>>> def f():
g()
>>> def g():
raise Exception, Exception(), None ## my traceback here
>>> f()
Traceback (most recent call last):
File "<pyshell#14>", line 1, in <module>
f()
File "<pyshell#8>", line 2, in f
g()
File "<pyshell#11>", line 2, in g
raise Exception, Exception(), None ## my traceback starts here
my traceback appears here
my traceback appears here
Exception
Impossible "Solutions": subclass and mock-object
>>> from types import *
>>> class CostomTB(TracebackType):
pass
Traceback (most recent call last):
File "<pyshell#125>", line 1, in <module>
class CostomTB(TracebackType):
TypeError: Error when calling the metaclass bases
type 'traceback' is not an acceptable base type
>>> class CostomTB(object):
pass
>>> try: zzzzzzzzz
except NameError:
import sys
ty, err, tb = sys.exc_info()
raise ty, err, CostomTB()
Traceback (most recent call last):
File "<pyshell#133>", line 5, in <module>
raise ty, err, CostomTB()
TypeError: raise: arg 3 must be a traceback or None
I am using python 2.7.
I guess you want the full traceback stack. See this which is having very good examples python logging module.
If some confusion comes See the logging documentation.
You mentioned a separate process: if your problem is to capture the traceback in process A and show it in process B, as if the exception was actually raised in the latter, then I'm afraid there is no clean way to do it.
I would suggest to serialize the traceback in process A, send it to process B and from there raise a new exception that includes the former in its description. The result is a somewhat longer output, but it carries information about both processes stacks.
In the following example there aren't really two separate processes, but I hope it makes my point clearer:
import traceback, StringI
def functionInProcessA():
raise Exception('Something happened in A')
class RemoteException(Exception):
def __init__(self, tb):
Exception.__init__(self, "Remote traceback:\n\n%s" % tb)
def controlProcessB():
try:
functionInProcessA()
except:
fd = StringIO.StringIO()
traceback.print_exc(file=fd)
tb = fd.getvalue()
raise RemoteException(tb)
if __name__ == '__main__':
controlProcessB()
Output:
Traceback (most recent call last):
File "a.py", line 20, in <module>
controlProcessB()
File "a.py", line 17, in controlProcessB
raise RemoteException(tb)
__main__.RemoteException: Remote traceback:
Traceback (most recent call last):
File "a.py", line 12, in controlProcessB
functionInProcessA()
File "a.py", line 4, in functionInProcessA
raise Exception('Something happened in A')
Exception: Something happened in A