Contents¶
Overview¶
docs |
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tests |
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package |
Serialization library for Exceptions and Tracebacks.
Free software: BSD license
It allows you to:
Pickle tracebacks and raise exceptions with pickled tracebacks in different processes. This allows better error handling when running code over multiple processes (imagine multiprocessing, billiard, futures, celery etc).
Create traceback objects from strings (the
from_string
method). No pickling is used.Serialize tracebacks to/from plain dicts (the
from_dict
andto_dict
methods). No pickling is used.Raise the tracebacks created from the aforementioned sources.
Pickle an Exception together with its traceback and exception chain (
raise ... from ...
) (Python 3 only)
Again, note that using the pickle support is completely optional. You are solely responsible for security problems should you decide to use the pickle support.
Installation¶
pip install tblib
Documentation¶
Pickling tracebacks¶
Note: The traceback objects that come out are stripped of some attributes (like variables). But you’ll be able to raise exceptions with those tracebacks or print them - that should cover 99% of the usecases.
>>> from tblib import pickling_support
>>> pickling_support.install()
>>> import pickle, sys
>>> def inner_0():
... raise Exception('fail')
...
>>> def inner_1():
... inner_0()
...
>>> def inner_2():
... inner_1()
...
>>> try:
... inner_2()
... except:
... s1 = pickle.dumps(sys.exc_info())
...
>>> len(s1) > 1
True
>>> try:
... inner_2()
... except:
... s2 = pickle.dumps(sys.exc_info(), protocol=pickle.HIGHEST_PROTOCOL)
...
>>> len(s2) > 1
True
>>> try:
... import cPickle
... except ImportError:
... import pickle as cPickle
>>> try:
... inner_2()
... except:
... s3 = cPickle.dumps(sys.exc_info(), protocol=pickle.HIGHEST_PROTOCOL)
...
>>> len(s3) > 1
True
Unpickling tracebacks¶
>>> pickle.loads(s1)
(<...Exception'>, Exception('fail'...), <traceback object at ...>)
>>> pickle.loads(s2)
(<...Exception'>, Exception('fail'...), <traceback object at ...>)
>>> pickle.loads(s3)
(<...Exception'>, Exception('fail'...), <traceback object at ...>)
Raising¶
>>> from six import reraise
>>> reraise(*pickle.loads(s1))
Traceback (most recent call last):
...
File "<doctest README.rst[14]>", line 1, in <module>
reraise(*pickle.loads(s2))
File "<doctest README.rst[8]>", line 2, in <module>
inner_2()
File "<doctest README.rst[5]>", line 2, in inner_2
inner_1()
File "<doctest README.rst[4]>", line 2, in inner_1
inner_0()
File "<doctest README.rst[3]>", line 2, in inner_0
raise Exception('fail')
Exception: fail
>>> reraise(*pickle.loads(s2))
Traceback (most recent call last):
...
File "<doctest README.rst[14]>", line 1, in <module>
reraise(*pickle.loads(s2))
File "<doctest README.rst[8]>", line 2, in <module>
inner_2()
File "<doctest README.rst[5]>", line 2, in inner_2
inner_1()
File "<doctest README.rst[4]>", line 2, in inner_1
inner_0()
File "<doctest README.rst[3]>", line 2, in inner_0
raise Exception('fail')
Exception: fail
>>> reraise(*pickle.loads(s3))
Traceback (most recent call last):
...
File "<doctest README.rst[14]>", line 1, in <module>
reraise(*pickle.loads(s2))
File "<doctest README.rst[8]>", line 2, in <module>
inner_2()
File "<doctest README.rst[5]>", line 2, in inner_2
inner_1()
File "<doctest README.rst[4]>", line 2, in inner_1
inner_0()
File "<doctest README.rst[3]>", line 2, in inner_0
raise Exception('fail')
Exception: fail
Pickling Exceptions together with their traceback and chain (Python 3 only)¶
>>> try:
... try:
... 1 / 0
... except Exception as e:
... raise Exception("foo") from e
... except Exception as e:
... s = pickle.dumps(e)
>>> raise pickle.loads(s)
Traceback (most recent call last):
File "<doctest README.rst[16]>", line 3, in <module>
1 / 0
ZeroDivisionError: division by zero
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "<doctest README.rst[17]>", line 1, in <module>
raise pickle.loads(s)
File "<doctest README.rst[16]>", line 5, in <module>
raise Exception("foo") from e
Exception: foo
BaseException subclasses defined after calling pickling_support.install()
will
not retain their traceback and exception chain pickling.
To cover custom Exceptions, there are three options:
Use
@pickling_support.install
as a decorator for each custom Exception>>> from tblib import pickling_support >>> # Declare all imports of your package's dependencies >>> import numpy >>> pickling_support.install() # install for all modules imported so far >>> @pickling_support.install ... class CustomError(Exception): ... pass
Eventual subclasses of
CustomError
will need to be decorated again.Invoke
pickling_support.install()
after all modules have been imported and all Exception subclasses have been declared>>> # Declare all imports of your package's dependencies >>> import numpy >>> from tblib import pickling_support >>> # Declare your own custom Exceptions >>> class CustomError(Exception): ... pass >>> # Finally, install tblib >>> pickling_support.install()
Selectively install tblib for Exception instances just before they are pickled
pickling_support.install(<Exception instance>, [Exception instance], ...)
The above will install tblib pickling for all listed exceptions as well as any other exceptions in their exception chains.
For example, one could write a wrapper to be used with ProcessPoolExecutor, Dask.distributed, or similar libraries:
>>> from tblib import pickling_support
>>> def wrapper(func, *args, **kwargs):
... try:
... return func(*args, **kwargs)
... except Exception as e:
... pickling_support.install(e)
... raise
What if we have a local stack, does it show correctly ?¶
Yes it does:
>>> exc_info = pickle.loads(s3)
>>> def local_0():
... reraise(*exc_info)
...
>>> def local_1():
... local_0()
...
>>> def local_2():
... local_1()
...
>>> local_2()
Traceback (most recent call last):
File "...doctest.py", line ..., in __run
compileflags, 1) in test.globs
File "<doctest README.rst[24]>", line 1, in <module>
local_2()
File "<doctest README.rst[23]>", line 2, in local_2
local_1()
File "<doctest README.rst[22]>", line 2, in local_1
local_0()
File "<doctest README.rst[21]>", line 2, in local_0
reraise(*exc_info)
File "<doctest README.rst[11]>", line 2, in <module>
inner_2()
File "<doctest README.rst[5]>", line 2, in inner_2
inner_1()
File "<doctest README.rst[4]>", line 2, in inner_1
inner_0()
File "<doctest README.rst[3]>", line 2, in inner_0
raise Exception('fail')
Exception: fail
It also supports more contrived scenarios¶
Like tracebacks with syntax errors:
>>> from tblib import Traceback
>>> from examples import bad_syntax
>>> try:
... bad_syntax()
... except:
... et, ev, tb = sys.exc_info()
... tb = Traceback(tb)
...
>>> reraise(et, ev, tb.as_traceback())
Traceback (most recent call last):
...
File "<doctest README.rst[58]>", line 1, in <module>
reraise(et, ev, tb.as_traceback())
File "<doctest README.rst[57]>", line 2, in <module>
bad_syntax()
File "...tests...examples.py", line 18, in bad_syntax
import badsyntax
File "...tests...badsyntax.py", line 5
is very bad
^
SyntaxError: invalid syntax
Or other import failures:
>>> from examples import bad_module
>>> try:
... bad_module()
... except:
... et, ev, tb = sys.exc_info()
... tb = Traceback(tb)
...
>>> reraise(et, ev, tb.as_traceback())
Traceback (most recent call last):
...
File "<doctest README.rst[61]>", line 1, in <module>
reraise(et, ev, tb.as_traceback())
File "<doctest README.rst[60]>", line 2, in <module>
bad_module()
File "...tests...examples.py", line 23, in bad_module
import badmodule
File "...tests...badmodule.py", line 3, in <module>
raise Exception("boom!")
Exception: boom!
Or a traceback that’s caused by exceeding the recursion limit (here we’re forcing the type and value to have consistency across platforms):
>>> def f(): f()
>>> try:
... f()
... except RuntimeError:
... et, ev, tb = sys.exc_info()
... tb = Traceback(tb)
...
>>> reraise(RuntimeError, RuntimeError("maximum recursion depth exceeded"), tb.as_traceback())
Traceback (most recent call last):
...
File "<doctest README.rst[32]>", line 1, in f
def f(): f()
File "<doctest README.rst[32]>", line 1, in f
def f(): f()
File "<doctest README.rst[32]>", line 1, in f
def f(): f()
...
RuntimeError: maximum recursion depth exceeded
Reference¶
tblib.Traceback¶
It is used by the pickling_support
. You can use it too if you want more flexibility:
>>> from tblib import Traceback
>>> try:
... inner_2()
... except:
... et, ev, tb = sys.exc_info()
... tb = Traceback(tb)
...
>>> reraise(et, ev, tb.as_traceback())
Traceback (most recent call last):
...
File "<doctest README.rst[21]>", line 6, in <module>
reraise(et, ev, tb.as_traceback())
File "<doctest README.rst[21]>", line 2, in <module>
inner_2()
File "<doctest README.rst[5]>", line 2, in inner_2
inner_1()
File "<doctest README.rst[4]>", line 2, in inner_1
inner_0()
File "<doctest README.rst[3]>", line 2, in inner_0
raise Exception('fail')
Exception: fail
tblib.Traceback.to_dict¶
You can use the to_dict
method and the from_dict
classmethod to
convert a Traceback into and from a dictionary serializable by the stdlib
json.JSONDecoder:
>>> import json
>>> from pprint import pprint
>>> try:
... inner_2()
... except:
... et, ev, tb = sys.exc_info()
... tb = Traceback(tb)
... tb_dict = tb.to_dict()
... pprint(tb_dict)
{'tb_frame': {'f_code': {'co_filename': '<doctest README.rst[...]>',
'co_name': '<module>'},
'f_globals': {'__name__': '__main__'},
'f_lineno': 5},
'tb_lineno': 2,
'tb_next': {'tb_frame': {'f_code': {'co_filename': ...,
'co_name': 'inner_2'},
'f_globals': {'__name__': '__main__'},
'f_lineno': 2},
'tb_lineno': 2,
'tb_next': {'tb_frame': {'f_code': {'co_filename': ...,
'co_name': 'inner_1'},
'f_globals': {'__name__': '__main__'},
'f_lineno': 2},
'tb_lineno': 2,
'tb_next': {'tb_frame': {'f_code': {'co_filename': ...,
'co_name': 'inner_0'},
'f_globals': {'__name__': '__main__'},
'f_lineno': 2},
'tb_lineno': 2,
'tb_next': None}}}}
tblib.Traceback.from_dict¶
Building on the previous example:
>>> tb_json = json.dumps(tb_dict)
>>> tb = Traceback.from_dict(json.loads(tb_json))
>>> reraise(et, ev, tb.as_traceback())
Traceback (most recent call last):
...
File "<doctest README.rst[21]>", line 6, in <module>
reraise(et, ev, tb.as_traceback())
File "<doctest README.rst[21]>", line 2, in <module>
inner_2()
File "<doctest README.rst[5]>", line 2, in inner_2
inner_1()
File "<doctest README.rst[4]>", line 2, in inner_1
inner_0()
File "<doctest README.rst[3]>", line 2, in inner_0
raise Exception('fail')
Exception: fail
tblib.Traceback.from_string¶
>>> tb = Traceback.from_string("""
... File "skipped.py", line 123, in func_123
... Traceback (most recent call last):
... File "tests/examples.py", line 2, in func_a
... func_b()
... File "tests/examples.py", line 6, in func_b
... func_c()
... File "tests/examples.py", line 10, in func_c
... func_d()
... File "tests/examples.py", line 14, in func_d
... Doesn't: matter
... """)
>>> reraise(et, ev, tb.as_traceback())
Traceback (most recent call last):
...
File "<doctest README.rst[42]>", line 6, in <module>
reraise(et, ev, tb.as_traceback())
File "...examples.py", line 2, in func_a
func_b()
File "...examples.py", line 6, in func_b
func_c()
File "...examples.py", line 10, in func_c
func_d()
File "...examples.py", line 14, in func_d
raise Exception("Guessing time !")
Exception: fail
If you use the strict=False
option then parsing is a bit more lax:
>>> tb = Traceback.from_string("""
... File "bogus.py", line 123, in bogus
... Traceback (most recent call last):
... File "tests/examples.py", line 2, in func_a
... func_b()
... File "tests/examples.py", line 6, in func_b
... func_c()
... File "tests/examples.py", line 10, in func_c
... func_d()
... File "tests/examples.py", line 14, in func_d
... Doesn't: matter
... """, strict=False)
>>> reraise(et, ev, tb.as_traceback())
Traceback (most recent call last):
...
File "<doctest README.rst[42]>", line 6, in <module>
reraise(et, ev, tb.as_traceback())
File "bogus.py", line 123, in bogus
File "...examples.py", line 2, in func_a
func_b()
File "...examples.py", line 6, in func_b
func_c()
File "...examples.py", line 10, in func_c
func_d()
File "...examples.py", line 14, in func_d
raise Exception("Guessing time !")
Exception: fail
tblib.decorators.return_error¶
>>> from tblib.decorators import return_error
>>> inner_2r = return_error(inner_2)
>>> e = inner_2r()
>>> e
<tblib.decorators.Error object at ...>
>>> e.reraise()
Traceback (most recent call last):
...
File "<doctest README.rst[26]>", line 1, in <module>
e.reraise()
File "...tblib...decorators.py", line 19, in reraise
reraise(self.exc_type, self.exc_value, self.traceback)
File "...tblib...decorators.py", line 25, in return_exceptions_wrapper
return func(*args, **kwargs)
File "<doctest README.rst[5]>", line 2, in inner_2
inner_1()
File "<doctest README.rst[4]>", line 2, in inner_1
inner_0()
File "<doctest README.rst[3]>", line 2, in inner_0
raise Exception('fail')
Exception: fail
How’s this useful? Imagine you’re using multiprocessing like this:
# Note that Python 3.4 and later will show the remote traceback (but as a string sadly) so we skip testing this.
>>> import traceback
>>> from multiprocessing import Pool
>>> from examples import func_a
>>> pool = Pool() # doctest: +SKIP
>>> try: # doctest: +SKIP
... for i in pool.map(func_a, range(5)):
... print(i)
... except:
... print(traceback.format_exc())
...
Traceback (most recent call last):
File "<doctest README.rst[...]>", line 2, in <module>
for i in pool.map(func_a, range(5)):
File "...multiprocessing...pool.py", line ..., in map
...
File "...multiprocessing...pool.py", line ..., in get
...
Exception: Guessing time !
<BLANKLINE>
>>> pool.terminate() # doctest: +SKIP
Not very useful is it? Let’s sort this out:
>>> from tblib.decorators import apply_with_return_error, Error
>>> from itertools import repeat
>>> pool = Pool()
>>> try:
... for i in pool.map(apply_with_return_error, zip(repeat(func_a), range(5))):
... if isinstance(i, Error):
... i.reraise()
... else:
... print(i)
... except:
... print(traceback.format_exc())
...
Traceback (most recent call last):
File "<doctest README.rst[...]>", line 4, in <module>
i.reraise()
File "...tblib...decorators.py", line ..., in reraise
reraise(self.exc_type, self.exc_value, self.traceback)
File "...tblib...decorators.py", line ..., in return_exceptions_wrapper
return func(*args, **kwargs)
File "...tblib...decorators.py", line ..., in apply_with_return_error
return args[0](*args[1:])
File "...examples.py", line 2, in func_a
func_b()
File "...examples.py", line 6, in func_b
func_c()
File "...examples.py", line 10, in func_c
func_d()
File "...examples.py", line 14, in func_d
raise Exception("Guessing time !")
Exception: Guessing time !
>>> pool.terminate()
Much better !
What if we have a local call stack ?¶
>>> def local_0():
... pool = Pool()
... try:
... for i in pool.map(apply_with_return_error, zip(repeat(func_a), range(5))):
... if isinstance(i, Error):
... i.reraise()
... else:
... print(i)
... finally:
... pool.close()
...
>>> def local_1():
... local_0()
...
>>> def local_2():
... local_1()
...
>>> try:
... local_2()
... except:
... print(traceback.format_exc())
Traceback (most recent call last):
File "<doctest README.rst[...]>", line 2, in <module>
local_2()
File "<doctest README.rst[...]>", line 2, in local_2
local_1()
File "<doctest README.rst[...]>", line 2, in local_1
local_0()
File "<doctest README.rst[...]>", line 6, in local_0
i.reraise()
File "...tblib...decorators.py", line 20, in reraise
reraise(self.exc_type, self.exc_value, self.traceback)
File "...tblib...decorators.py", line 27, in return_exceptions_wrapper
return func(*args, **kwargs)
File "...tblib...decorators.py", line 47, in apply_with_return_error
return args[0](*args[1:])
File "...tests...examples.py", line 2, in func_a
func_b()
File "...tests...examples.py", line 6, in func_b
func_c()
File "...tests...examples.py", line 10, in func_c
func_d()
File "...tests...examples.py", line 14, in func_d
raise Exception("Guessing time !")
Exception: Guessing time !
Other weird stuff¶
Clearing traceback works (Python 3.4 and up):
>>> tb = Traceback.from_string("""
... File "skipped.py", line 123, in func_123
... Traceback (most recent call last):
... File "tests/examples.py", line 2, in func_a
... func_b()
... File "tests/examples.py", line 6, in func_b
... func_c()
... File "tests/examples.py", line 10, in func_c
... func_d()
... File "tests/examples.py", line 14, in func_d
... Doesn't: matter
... """)
>>> import traceback, sys
>>> if sys.version_info > (3, 4):
... traceback.clear_frames(tb)
Credits¶
mitsuhiko/jinja2 for figuring a way to create traceback objects.
Installation¶
At the command line:
pip install tblib
Usage¶
To use tblib in a project:
import tblib
Contributing¶
Contributions are welcome, and they are greatly appreciated! Every little bit helps, and credit will always be given.
Bug reports¶
When reporting a bug please include:
Your operating system name and version.
Any details about your local setup that might be helpful in troubleshooting.
Detailed steps to reproduce the bug.
Documentation improvements¶
tblib could always use more documentation, whether as part of the official tblib docs, in docstrings, or even on the web in blog posts, articles, and such.
Feature requests and feedback¶
The best way to send feedback is to file an issue at https://github.com/ionelmc/python-tblib/issues.
If you are proposing a feature:
Explain in detail how it would work.
Keep the scope as narrow as possible, to make it easier to implement.
Remember that this is a volunteer-driven project, and that code contributions are welcome :)
Development¶
To set up python-tblib for local development:
Fork python-tblib (look for the “Fork” button).
Clone your fork locally:
git clone git@github.com:YOURGITHUBNAME/python-tblib.git
Create a branch for local development:
git checkout -b name-of-your-bugfix-or-feature
Now you can make your changes locally.
When you’re done making changes run all the checks and docs builder with tox one command:
tox
Commit your changes and push your branch to GitHub:
git add . git commit -m "Your detailed description of your changes." git push origin name-of-your-bugfix-or-feature
Submit a pull request through the GitHub website.
Pull Request Guidelines¶
If you need some code review or feedback while you’re developing the code just make the pull request.
For merging, you should:
Include passing tests (run
tox
).Update documentation when there’s new API, functionality etc.
Add a note to
CHANGELOG.rst
about the changes.Add yourself to
AUTHORS.rst
.
Tips¶
To run a subset of tests:
tox -e envname -- pytest -k test_myfeature
To run all the test environments in parallel:
tox -p auto
API Reference¶
This page contains auto-generated API reference documentation 1.
tblib
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Submodules¶
tblib.decorators
¶
Module Contents¶
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args is a tuple where the first argument is a callable. |
tblib.pickling_support
¶
Module Contents¶
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Package Contents¶
Classes¶
Class that replicates just enough of the builtin Code object to enable serialization and traceback rendering. |
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Class that replicates just enough of the builtin Frame object to enable serialization and traceback rendering. |
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Class that wraps builtin Traceback objects. |
- exception tblib.TracebackParseError[source]¶
Bases:
Exception
Common base class for all non-exit exceptions.
- class tblib.Code(code)[source]¶
Class that replicates just enough of the builtin Code object to enable serialization and traceback rendering.
- co_code¶
- class tblib.Frame(frame)[source]¶
Class that replicates just enough of the builtin Frame object to enable serialization and traceback rendering.
- class tblib.Traceback(tb)[source]¶
Class that wraps builtin Traceback objects.
- tb_next¶
- to_traceback¶
- to_dict¶
- as_traceback()[source]¶
Convert to a builtin Traceback object that is usable for raising or rendering a stacktrace.
- as_dict()[source]¶
Converts to a dictionary representation. You can serialize the result to JSON as it only has builtin objects like dicts, lists, ints or strings.
- 1
Created with sphinx-autoapi
Changelog¶
2.0.0 (2023-06-22)¶
Removed support for legacy Pythons (2.7 and 3.6) and added Python 3.11 in the test grid.
Some cleanups and refactors (mostly from ruff).
1.7.0 (2020-07-24)¶
Add more attributes to
Frame
andCode
objects for pytest compatibility. Contributed by Ivanq in #58.
1.6.0 (2019-12-07)¶
When pickling an Exception, also pickle its traceback and the Exception chain (
raise ... from ...
). Contributed by Guido Imperiale in #53.
1.5.0 (2019-10-23)¶
Added support for Python 3.8. Contributed by Victor Stinner in #42.
Removed support for end of life Python 3.4.
Few CI improvements and fixes.
1.4.0 (2019-05-02)¶
Removed support for end of life Python 3.3.
Fixed tests for Python 3.7. Contributed by Elliott Sales de Andrade in #36.
Fixed compatibility issue with Twised (
twisted.python.failure.Failure
expected aco_code
attribute).
1.3.2 (2017-04-09)¶
Add support for PyPy3.5-5.7.1-beta. Previously
AttributeError: 'Frame' object has no attribute 'clear'
could be raised. See PyPy issue #2532.
1.3.1 (2017-03-27)¶
Fixed handling for tracebacks due to exceeding the recursion limit. Fixes #15.
1.3.0 (2016-03-08)¶
Added
Traceback.from_string
.
1.2.0 (2015-12-18)¶
1.1.0 (2015-07-27)¶
Added support for Python 2.6. Contributed by Arcadiy Ivanov in #8.
1.0.0 (2015-03-30)¶
Added
to_dict
method andfrom_dict
classmethod on Tracebacks. Contributed by beckjake in #5.