I have two separate processes client.py and service.py. I communicate between the two using json serializing format. Suppose service.py raises an exception and I collect the exception object like so:
service.py
import sys
import traceback
try:
1/0
except ZeroDivisionError:
ex_typ, ex, tb = sys.exc_info()
exc_st = traceback.format_exception(ex_typ, ex, tb)
exc_st = "\n".join(exc_st)
because I have to send the result over the wire I will serialze it like:
import json
res = {"result": [str(ex_typ), exc_st]}
json.dumps(res)
Now, I want to re-raise the same exception in the client.py module/process, currently I workaround is some thing like
import json
exc_typ, exc_st = json.loads(res)["result"]
I am not sure how can I convert exc_typ which is in str format to actual exception type(ZeroDivisionError) and raise with exc_st stacktrace (which should only holds service module traceback)?
Could someone share their thoughts?
Cheers,
DD.
I have a Django ORM query like this:
try:
specialization_object = Specialization.objects.get(name="My Test Specialization")
except Exception as ex:
print(ex)
When there occurs an exception then it prints "Specialization matching query does not exist.", but it does not print the line number. How can I trace the line number on which the exception or error occurred?
try this:
import logging
logger = logging.getLogger(__name__)
try:
specialization_object = Specialization.objects.get(name="My Test Specialization")
except Exception as ex:
logger.info(ex, exc_info=True) # exc_info will add traceback
further reading see here
If you can't for any reason use logging, There's the standard package traceback, and you can do something like:
traceback.print_exc(file=sys.stdout)
I have figured out a simple solution just now:
import traceback
try:
specialization_object = Specialization.objects.get(name="My Test Specialization")
except Exception as ex:
print(traceback.format_exc())
I have an error which I have a little difficulty understanding. I have a script which uses biopython to query a database. Sometimes, biopython can't find what we're looking for, and an HTTPError is thrown. I cannot, however catch the HTTPError, as I get the following error message:
HTTPError: HTTP Error 404: Not Found
During handling of the above exception, another exception occurred:
NameError Traceback (most recent call
last) in ()
51 UniProt = text[index+9:index+15]
52 uniprot_IDs[bigg_ID] = UniProt
---> 53 except HTTPError:
54 if err.code == '404':
55 uniprot_IDs[biGG_ID] = None
NameError: name 'HTTPError' is not defined
How can an error which is not defined be thrown in the first place? What am I missing?
This is the relevant code:
from Bio.KEGG import REST, Enzyme
from DataTreatment import openJson, write
...
try:
ec_number = some_string
text = REST.kegg_get('ec:'+ec_number).read()
...
except HTTPError:
if err.code == '404':
a_dict[a_key] = None
You need to import the HTTPError class. If you already imported, then make sure you got the right one. You can try to catch with a generic Exception and use type(ex) to find out which it is and import the correct type.
You need to import the HTTPError-class, try this;
In the top of your code, add
from urllib.error import HTTPError
Source: Entrez._HTTPError vs. Entrez.HTTPError (via Entrez.efetch)
With code like the snippet below, we can catch AWS exceptions:
from aws_utils import make_session
session = make_session()
cf = session.resource("iam")
role = cf.Role("foo")
try:
role.load()
except Exception as e:
print(type(e))
raise e
The returned error is of type botocore.errorfactory.NoSuchEntityException. However, when I try to import this exception, I get this:
>>> import botocore.errorfactory.NoSuchEntityException
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named NoSuchEntityException
The best method I could find of catching this specific error is:
from botocore.exceptions import ClientError
session = make_session()
cf = session.resource("iam")
role = cf.Role("foo")
try:
role.load()
except ClientError as e:
if e.response["Error"]["Code"] == "NoSuchEntity":
# ignore the target exception
pass
else:
# this is not the exception we are looking for
raise e
But this seems very "hackish". Is there a way to directly import and catch specific subclasses of ClientError in boto3?
EDIT: Note that if you catch errors in the second way and print the type, it will be ClientError.
If you're using the client you can catch the exceptions like this:
import boto3
def exists(role_name):
client = boto3.client('iam')
try:
client.get_role(RoleName='foo')
return True
except client.exceptions.NoSuchEntityException:
return False
If you're using the resource you can catch the exceptions like this:
cf = session.resource("iam")
role = cf.Role("foo")
try:
role.load()
except cf.meta.client.exceptions.NoSuchEntityException:
# ignore the target exception
pass
This combines the earlier answer with the simple trick of using .meta.client to get from the higher-level resource to the lower-level client (source: https://boto3.amazonaws.com/v1/documentation/api/latest/guide/clients.html#creating-clients).
try:
something
except client.exceptions.NoSuchEntityException:
something
This worked for me
I'm using python to evaluate some measured data. Because of many possible results it is difficult to handle or possible combinations. Sometimes an error happens during the evaluation. It is usually an index error because I get out of range from measured data.
It is very difficult to find out on which place in code the problem happened. It would help a lot if I knew on which line the error was raised. If I use following code:
try:
result = evaluateData(data)
except Exception, err:
print ("Error: %s.\n" % str(err))
Unfortunately this only tells me that there is and index error. I would like to know more details about the exception (line in code, variable etc.) to find out what happened. Is it possible?
Thank you.
Solution, printing filename, linenumber, line itself and exception description:
import linecache
import sys
def PrintException():
exc_type, exc_obj, tb = sys.exc_info()
f = tb.tb_frame
lineno = tb.tb_lineno
filename = f.f_code.co_filename
linecache.checkcache(filename)
line = linecache.getline(filename, lineno, f.f_globals)
print 'EXCEPTION IN ({}, LINE {} "{}"): {}'.format(filename, lineno, line.strip(), exc_obj)
try:
print 1/0
except:
PrintException()
Output:
EXCEPTION IN (D:/Projects/delme3.py, LINE 15 "print 1/0"): integer division or modulo by zero
To simply get the line number you can use sys, if you would like to have more, try the traceback module.
import sys
try:
[][2]
except IndexError:
print("Error on line {}".format(sys.exc_info()[-1].tb_lineno))
prints:
Error on line 3
Example from the traceback module documentation:
import sys, traceback
def lumberjack():
bright_side_of_death()
def bright_side_of_death():
return tuple()[0]
try:
lumberjack()
except IndexError:
exc_type, exc_value, exc_traceback = sys.exc_info()
print "*** print_tb:"
traceback.print_tb(exc_traceback, limit=1, file=sys.stdout)
print "*** print_exception:"
traceback.print_exception(exc_type, exc_value, exc_traceback,
limit=2, file=sys.stdout)
print "*** print_exc:"
traceback.print_exc()
print "*** format_exc, first and last line:"
formatted_lines = traceback.format_exc().splitlines()
print formatted_lines[0]
print formatted_lines[-1]
print "*** format_exception:"
print repr(traceback.format_exception(exc_type, exc_value,
exc_traceback))
print "*** extract_tb:"
print repr(traceback.extract_tb(exc_traceback))
print "*** format_tb:"
print repr(traceback.format_tb(exc_traceback))
print "*** tb_lineno:", exc_traceback.tb_lineno
I use the traceback which is simple and robust:
import traceback
try:
raise ValueError()
except:
print(traceback.format_exc()) # or: traceback.print_exc()
Out:
Traceback (most recent call last):
File "catch.py", line 4, in <module>
raise ValueError()
ValueError
The simplest way is just to use:
import traceback
try:
<blah>
except IndexError:
traceback.print_exc()
or if using logging:
import logging
try:
<blah>
except IndexError as e:
logging.exception(e)
Gives you file, lineno, and exception for the last item in the call stack
from sys import exc_info
from traceback import format_exception
def print_exception():
etype, value, tb = exc_info()
info, error = format_exception(etype, value, tb)[-2:]
print(f'Exception in:\n{info}\n{error}')
try:
1 / 0
except:
print_exception()
prints
Exception in:
File "file.py", line 12, in <module>
1 / 0
ZeroDivisionError: division by zero
I would suggest using the python logging library, it has two useful methods that might help in this case.
logging.findCaller()
findCaller(stack_info=False) - Reports just the line number for the previous caller leading to the exception raised
findCaller(stack_info=True) - Reports the line number & stack for the previous caller leading to the exception raised
logging.logException()
Reports the line & stack within the try/except block that raised the exception
For more info checkout the api https://docs.python.org/3/library/logging.html
There are many answers already posted here that show how to get the line number, but it's worth noting that if you want variables containing the "raw data," so to speak, of the stack trace so that you can have more granular control of what you display or how you format it, using the traceback module you can step through the stack frame by frame and look at what's stored in the attributes of the frame summary objects. There are several simple and elegant ways to manipulate the frame summary objects directly. Let's say for example that you want the line number from the last frame in the stack (which tells you which line of code triggered the exception), here's how you could get it by accessing the relevant frame summary object:
Option 1:
import sys
import traceback
try:
# code that raises an exception
except Exception as exc:
exc_type, exc_value, exc_tb = sys.exc_info()
stack_summary = traceback.extract_tb(exc_tb)
end = stack_summary[-1] # or `stack_summary.pop(-1)` if you prefer
Option 2:
import sys
import traceback
try:
# code that raises an exception
except Exception as exc:
tbe = traceback.TracebackException(*sys.exc_info())
end = tbe.stack[-1] # or `tbe.stack.pop(-1)` if you prefer
In either of the above examples, end will be a frame summary object:
>>> type(end)
<class 'traceback.FrameSummary'>
which was in turn taken from a stack summary object:
>>> type(stack_summary) # from option 1
<class 'traceback.StackSummary'>
>>> type(tbe.stack) # from option 2
<class 'traceback.StackSummary'>
The stack summary object behaves like a list and you can iterate through all of the frame summary objects in it however you want in order to trace through the error. The frame summary object (end, in this example), contains the line number and everything else you need to locate where in the code the exception occurred:
>>> print(end.__doc__)
A single frame from a traceback.
- :attr:`filename` The filename for the frame.
- :attr:`lineno` The line within filename for the frame that was
active when the frame was captured.
- :attr:`name` The name of the function or method that was executing
when the frame was captured.
- :attr:`line` The text from the linecache module for the
of code that was running when the frame was captured.
- :attr:`locals` Either None if locals were not supplied, or a dict
mapping the name to the repr() of the variable.
And if you capture the exception object (either from except Exception as exc: syntax or from the second object returned by sys.exc_info()), you will then have everything you need to write your own highly customized error printing/logging function:
err_type = type(exc).__name__
err_msg = str(exc)
Putting it all together:
from datetime import datetime
import sys
import traceback
def print_custom_error_message():
exc_type, exc_value, exc_tb = sys.exc_info()
stack_summary = traceback.extract_tb(exc_tb)
end = stack_summary[-1]
err_type = type(exc_value).__name__
err_msg = str(exc_value)
date = datetime.strftime(datetime.now(), "%B %d, %Y at precisely %I:%M %p")
print(f"On {date}, a {err_type} occured in {end.filename} inside {end.name} on line {end.lineno} with the error message: {err_msg}.")
print(f"The following line of code is responsible: {end.line!r}")
print("Please make a note of it.")
def do_something_wrong():
try:
1/0
except Exception as exc:
print_custom_error_message()
if __name__ == "__main__":
do_something_wrong()
Let's run it!
user#some_machine:~$ python example.py
On August 25, 2022 at precisely 01:31 AM, a ZeroDivisionError occured in example.py inside do_something_wrong on line 21 with the error message: division by zero.
The following line of code is responsible: '1/0'
Please make a note of it.
At this point you can see how you could print this message for any place in the stack: end, beginning, anywhere in-between, or iterate through and print it for every frame in the stack.
Of course, the formatting functionality already provided by the traceback module covers most debugging use cases, but it's useful to know how to manipulate the traceback objects to extract the information you want.
I always use this snippet
import sys, os
try:
raise NotImplementedError("No error")
except Exception as e:
exc_type, exc_obj, exc_tb = sys.exc_info()
fname = os.path.split(exc_tb.tb_frame.f_code.co_filename)[1]
print(exc_type, fname, exc_tb.tb_lineno)
for different views and possible issues you can refer When I catch an exception, how do I get the type, file, and line number?
All the solutions answer the OPs problem, however, if one is holding onto a specific error instance and the last traceback stack won't do it they will not suffice —a corner scenario example given below.
In this case, the magic attribute __traceback__ of a raised exception instance may be used. This is a system traceback object (exposed as types.TracebackType, see Types) not the module. This traceback instance behaves just one like would expect (but it is always nice to check):
from collections import deque
from typing import (List, )
errors: List[Exception] = deque([], 5)
def get_raised(error_cls: type, msg: str) -> Exception:
# for debugging, an exception instance that is not raised
# ``__traceback__`` has ``None``
try:
raise error_cls(msg)
except Exception as error:
return error
error = get_raised(NameError, 'foo')
errors.append(error)
error = get_raised(ValueError, 'bar')
errors.append(error)
try:
raise get_raised(TypeError, 'bar')
except Exception as error:
errors.append(error)
Now, I can check out the first error's details:
import types
traceback = errors[0].__traceback__ # inadvisable name due to module
line_no: int = traceback.tb_lineno
frame: types.FrameType = traceback.tb_frame
previous: Union[type(None), types.TracebackType] = traceback.tb_next
filename: str = frame.f_code.co_filename
The traceback's previous is None for the second error despite a preceding error as expected, but for the third wherein an error is raised twice it is not.
This below is just a test which makes no sense contextually. A case were it is useful if when an exception is raised in a view of a webapp (a 500 status kind of incident) that gets caught and stored for the admit to inspect akin to Setry.io (but for free). Here is a minimal example where the home page / will raise an error, that gets caught and the route errors will list them. This is using Pyramid in a very concentrated way (multifile is way better) with no logging or authentication and the error logging could be better for the admin to inspect similar to Sentry.io.
from pyramid.config import Configurator
from waitress import serve
from collections import deque
# just for typehinting:
from pyramid.request import Request
from pyramid.traversal import DefaultRootFactory
from pyramid.router import Router
import types
from typing import (List, )
def home_view(context: DefaultRootFactory, request: Request) -> dict:
raise NotImplementedError('I forgot to fill this')
return {'status': 'ok'} # never reached.
def caught_view(error: Exception, request: Request) -> dict:
"""
Exception above is just type hinting.
This is controlled by the context argument in
either the ``add_exception_view`` method of config,
or the ``exception_view_config`` decorator factory (callable class)
"""
# this below is a simplification as URLDecodeError is an attack (418)
request.response.status = 500
config.registry.settings['error_buffer'].append(error)
#logging.exception(error) # were it set up.
#slack_admin(format_error(error)) # ditto
return {'status': 'error', 'message': 'The server crashed!!'}
def format_error(error: Exception) -> str:
traceback = error.__traceback__ # inadvisable name due to module
frame: types.FrameType = traceback.tb_frame
return f'{type(error).__name__}: {error}' +\
f'at line {traceback.tb_lineno} in file {frame.f_code.co_filename}'
def error_view(context: DefaultRootFactory, request: Request) -> dict:
print(request.registry.settings['error_buffer'])
return {'status': 'ok',
'errors':list(map(format_error, request.registry.settings['error_buffer']))
}
with Configurator(settings=dict()) as config:
config.add_route('home', '/')
config.add_route('errors', '/errors')
config.add_view(home_view, route_name='home', renderer='json')
config.add_view(error_view, route_name='errors', renderer='json')
config.add_exception_view(caught_view, context=Exception, renderer='json')
config.registry.settings['error_buffer']: List[Exception] = deque([], 5)
# not in config.registry.settings, not JSON serialisable
# config.add_request_method
app : Router = config.make_wsgi_app()
port = 6969
serve(app, port=port)