raise_from breaks on PY3 when the base exception has multiple arguments

[Antar1011]

Consider the following code:

from future.utils import raise_from

class MyException(Exception):

    def __init__(self, a, b):
        super(MyException, self).__init__('{0}: {1}'.format(a,7))

def foo():

    raise MyException(3, 7)

def bar():

    try:
        foo()
    except Exception as err:
        raise_from(ValueError('blue'), err)

Calling bar() works fine on PY2, but on PY3, one gets:

Traceback (most recent call last):
  File "blah.py", line 15, in bar
    foo()
  File "blah.py", line 10, in foo
    raise MyException(3, 7)
__main__.MyException: 3: 7

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "blah.py", line 27, in <module>
    bar()
  File "blah.py", line 17, in bar
    raise_from(ValueError('blue'), err)
  File "/Users/antar/Programming/.miniconda3/envs/futuristic/lib/python3.5/site-packages/future/utils/__init__.py", line 399, in raise_from
    exec(execstr, myglobals, mylocals)
  File "<string>", line 1, in <module>
TypeError: __init__() missing 1 required positional argument: 'b'

Basically, it looks like when future tries to re-create the exception, all it can do is parse the arguments as a single string (similar issue to #213).

[Daenyth]

Dupe #234?

[edschofield]

I think this is now fixed in v0.16.0. Please feel to re-open this if you notice any more problems. Thanks for reporting the bug!