15.21 診斷分析代碼錯誤

問題

The interpreter violently crashes with a segmentation fault, bus error, access violation,or other fatal error. You would like to get a Python traceback that shows you where yourprogram was running at the point of failure.

解決方案

The faulthandler module can be used to help you solve this problem. Include thefollowing code in your program:

import faulthandlerfaulthandler.enable()

Alternatively, run Python with the -Xfaulthandler option such as this:

bash % python3 -Xfaulthandler program.py

Last, but not least, you can set the PYTHONFAULTHANDLER environment variable.With faulthandler enabled, fatal errors in C extensions will result in a Python trace‐back being printed on failures. For example:

Fatal Python error: Segmentation fault

Current thread 0x00007fff71106cc0:File “example.py”, line 6 in fooFile “example.py”, line 10 in barFile “example.py”, line 14 in spamFile “example.py”, line 19 in > Segmentation fault

Although this won’t tell you where in the C code things went awry, at least it can tell youhow it got there from Python.

討論

The faulthandler will show you the stack traceback of the Python code executing atthe time of failure. At the very least, this will show you the top-level extension functionthat was invoked. With the aid of pdb or other Python debugger, you can investigate theflow of the Python code leading to the error.faulthandler will not tell you anything about the failure from C. For that, you willneed to use a traditional C debugger, such as gdb. However, the information from thefaulthandler traceback may give you a better idea of where to direct your attention.It should be noted that certain kinds of errors in C may not be easily recoverable. Forexample, if a C extension trashes the stack or program heap, it may render faulthandler inoperable and you’ll simply get no output at all (other than a crash). Obviously,your mileage may vary.