Pdb在异常中转到异常框架

Question

我正在使用pdb调试一个名为a.py的程序

def f(x) :
    x / x

def g(x) :
    try :
        f(x)
    except Exception as e :
        assert 0

g(0)

当我使用python3 -m pdb a.py运行程序时，程序在assert 0行停止，我得到以下错误信息：

Traceback (most recent call last):
  File "/tmp/a.py", line 6, in g
    f(x)
  File "/tmp/a.py", line 2, in f
    x / x
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib64/python3.6/pdb.py", line 1667, in main
    pdb._runscript(mainpyfile)
  File "/usr/lib64/python3.6/pdb.py", line 1548, in _runscript
    self.run(statement)
  File "/usr/lib64/python3.6/bdb.py", line 434, in run
    exec(cmd, globals, locals)
  File "<string>", line 1, in <module>
  File "/tmp/a.py", line 11, in <module>
    g(0)
  File "/tmp/a.py", line 9, in g
    assert 0
AssertionError

并且堆栈是（使用bt命令显示）：

(Pdb) bt
  /usr/lib64/python3.6/pdb.py(1667)main()
-> pdb._runscript(mainpyfile)
  /usr/lib64/python3.6/pdb.py(1548)_runscript()
-> self.run(statement)
  /usr/lib64/python3.6/bdb.py(434)run()
-> exec(cmd, globals, locals)
  <string>(1)<module>()->None
  /tmp/a.py(11)<module>()->None
-> g(0)
> /tmp/a.py(9)g()
-> assert 0
(Pdb) 

问题是，我不能简单地使用x / x和up去函数f调试down，因为我的堆栈结束于g函数。

我应该如何在异常中调试此类异常？异常中的异常例外情况怎么样？

Answer 1

在我看来，你有几个选择。您可以将try-except移动到f(x)，在g() try-except中打印描述性错误并放入pdb，或者在记录友好错误消息后重新引发异常。我不喜欢依赖未捕获的异常来调试（选项3），所以这里是选项1和2的样子：

'''Option 1'''
def f(x) :
    try:
        x / x
    except Exception as e:
        print('An error occurred, entering pdb shell')
        import pdb; pdb.set_trace()

def g(x) :
    f(x)

g(0)

输出：

$ python throw.py 
An error occurred, entering pdb shell
--Return--
> /home/wholevinski/so_test/throw.py(6)f()->None
-> import pdb; pdb.set_trace()
(Pdb) x
0

要么：

'''Option 2'''
def f(x):
    x / x

def g(x):
    try:
        f(x)
    except Exception as e:
        print('f({}) raised with error "{}". Entering pdb shell.'.format(x, str(e)))
        import pdb; pdb.set_trace()

g(0)

输出：

$ python throw.py 
f(0) raised with error division by zero. Entering pdb shell.
--Return--
> /home/wholevinski/so_test/throw.py(9)g()->None
-> import pdb; pdb.set_trace()
(Pdb) x

Answer 2

实际上重新引发异常（ wholevinski的answer中的选项3）解决了我的问题，因为它不需要我修改函数f。这是代码：

'''Option 3'''
def f(x) :
    x -= 1
    x / x

def g(x) :
    try :
        for i in range(x, 0, -1) :
            print(f(i))
    except Exception as e :
        raise e

g(10)

堆栈的Pdb输出：

(Pdb) bt
  /usr/lib64/python3.6/pdb.py(1667)main()
-> pdb._runscript(mainpyfile)
  /usr/lib64/python3.6/pdb.py(1548)_runscript()
-> self.run(statement)
  /usr/lib64/python3.6/bdb.py(434)run()
-> exec(cmd, globals, locals)
  <string>(1)<module>()->None
  /tmp/a.py(13)<module>()->None
-> g(10)
  /tmp/a.py(11)g()
-> raise e
  /tmp/a.py(9)g()
-> print(f(i))
> /tmp/a.py(4)f()
-> x / x
(Pdb)