How do I recover an older traceback in python? (eg second to last)

Question

I'm sure you found yourself in this situation, and I suspect there is no way out of this. Suppose you run some python code that raises an exception, then you want to look into it but accidentally raise another exception while doing so. If you try postmortem debugging now, you'll see the traceback of the latter exception. My question is, is the former lost forever?

Example:

def my_buggy_function(x):
    y = x + 1
    raise RuntimeError

Step 1: I raise an error and I want to debug it

my_buggy_function(1)


---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
/home/user/<ipython-input-1-430423eaff77> in <module>()
      3     raise RuntimeError
      4 
----> 5 my_buggy_function(1)

/home/user/<ipython-input-1-430423eaff77> in my_buggy_function(x)
      1 def my_buggy_function(x):
      2     y = x + 1
----> 3     raise RuntimeError
      4 
      5 my_buggy_function(1)

 RuntimeError: 

Step 2: I try to debug the error but accidentally raise another one (in this case, I did not load pdb)

 pdb.pm() #Oops..

 ---------------------------------------------------------------------------
 NameError                                 Traceback (most recent call last)
 /home/user/<ipython-input-2-619d77b83f20> in <module>()
 ----> 1 pdb.pm()

 NameError: name 'pdb' is not defined

 import pdb 

Step 3: Now the traceback gives me the last error, and the second to last is lost.

 pdb.traceback.print_last()
 Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/IPython/core/interactiveshell.py", line  2538, in run_code
    exec code_obj in self.user_global_ns, self.user_ns
  File "<ipython-input-1-619d77b83f20>", line 1, in <module>
   pdb.pm()
 NameError: name 'pdb' is not defined

What if I want to access y in the second-to-last traceback, is it lost forever?

Note: I'm using ipython/ipdb in case it matters

Answer 1

Exception chaining is only available in Python 3. It is not available in the 2.X series.

See this answer for more details: https://stackoverflow.com/a/16414892/1055722

EDIT: Reading more closely, you aren't talking about two nested exceptions but about one following another?

In that case you could use sys.excepthook to capture and store somewhere the last 10 exceptions (for example) so that you can look at the exception history from pdb.