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Diffstat (limited to 'Doc/howto')
| -rw-r--r-- | Doc/howto/pyporting.rst | 21 |
1 files changed, 13 insertions, 8 deletions
diff --git a/Doc/howto/pyporting.rst b/Doc/howto/pyporting.rst index f48f313..38a13af 100644 --- a/Doc/howto/pyporting.rst +++ b/Doc/howto/pyporting.rst @@ -587,14 +587,19 @@ exception to:: You can get more information about the raised exception from :func:`sys.exc_info` than simply the current exception instance, but you most -likely don't need it. One very key point to understand, though, is **do not -save the traceback to a variable without deleting it**! Because tracebacks -contain references to the current executing frame you will inadvertently create -a circular reference, prevent everything in the frame from being garbage -collected. This can be a massive memory leak if you are not careful. Simply -index into the returned value from :func:`sys.version_info` instead of -assigning the tuple it returns to a variable. - +likely don't need it. + +.. note:: + In Python 3, the traceback is attached to the exception instance + through the **__traceback__** attribute. If the instance is saved in + a local variable that persists outside of the ``except`` block, the + traceback will create a reference cycle with the current frame and its + dictionary of local variables. This will delay reclaiming dead + resources until the next cyclic :term:`garbage collection` pass. + + In Python 2, this problem only occurs if you save the traceback itself + (e.g. the third element of the tuple returned by :func:`sys.exc_info`) + in a variable. Other Resources =============== |