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Description:

pyodidetblib 1.7.1

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 and to_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
Unpickling tracebacks
Raising
Pickling Exceptions together with their traceback and chain (Python 3 only)

What if we have a local stack, does it show correctly ?
It also supports more contrived scenarios

Reference

tblib.Traceback

tblib.Traceback.to_dict
tblib.Traceback.from_dict
tblib.Traceback.from_string

tblib.decorators.return_error

What if we have a local call stack ?
Other weird stuff

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: # doctest: +SKIP
... try:
... 1 / 0
... except Exception as e:
... raise Exception("foo") from e
... except Exception as e:
... s = pickle.dumps(e)
>>> raise pickle.loads(s) # doctest: +SKIP
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 # doctest: +SKIP

>>> 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 # doctest: +SKIP
>>> 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 !
<BLANKLINE>
>>> 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 !
<BLANKLINE>

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.

Changelog

1.7.1 (2022-08-05)

Added pickling of __tracebackhide__ variable in locals for compatibility
with pytest stack frame suppression.

1.7.0 (2020-07-24)

Add more attributes to Frame and Code 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 a co_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)

Fixed handling for tracebacks from generators and other internal improvements
and optimizations. Contributed by DRayX in #10
and #11.

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 and from_dict classmethod on Tracebacks.
Contributed by beckjake in #5.