Here's a bit of sample code from [https://www.python.org/dev/peps/pep-3134/](PEP 3134):
class DatabaseError(Exception):
pass
class FileDatabase(object):
def __init__(self, filename):
try:
self.file = open(filename)
except IOError as exc:
raise DatabaseError('failed to open') from exc
fd = FileDatabase('dne')This, of course, does not work on Python 2. Using Python 3 I get the following output:
Traceback (most recent call last):
File "pepex2.py", line 7, in __init__
self.file = open(filename)
FileNotFoundError: [Errno 2] No such file or directory: 'dne'
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "pepex2.py", line 11, in <module>
fd = FileDatabase('dne')
File "pepex2.py", line 9, in __init__
raise DatabaseError('failed to open') from exc
__main__.DatabaseError: failed to open
When using raise_from for Python2 compatibility
from future.utils import raise_from
# [...]
raise_from(DatabaseError('failed to open'), exc)this output (still with Python3) changes to:
FileNotFoundError: [Errno 2] No such file or directory
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "pepex2.py", line 13, in <module>
fd = FileDatabase('dne')
File "pepex2.py", line 11, in __init__
raise_from(DatabaseError('failed to open'), exc)
File "/home/marc/.virtualenvs/scratch_future3/lib/python3.3/site-packages/future/utils/__init__.py", line 382, in raise_from
exec(execstr, myglobals, mylocals)
File "<string>", line 1, in <module>
__main__.DatabaseError: failed to open
Note that the traceback and exception information are missing from the FileNotFoundError.
Here's a bit of sample code from [https://www.python.org/dev/peps/pep-3134/](PEP 3134):
This, of course, does not work on Python 2. Using Python 3 I get the following output:
When using
raise_fromfor Python2 compatibilitythis output (still with Python3) changes to:
Note that the traceback and exception information are missing from the
FileNotFoundError.