Caught exception is None

Question

I have a script written in python2.7 where I, for debugging purposes, use a catch-all statement to catch and print all exceptions. For some reason, the exception caught is sometimes None. What could cause this to happen?

the code is something like this:

from __future__ import print_function

try:
    run_arbitrary_code()
except Exception as e:
    print(e)

The output is then:

None
None
None
None

I have never experienced an exception being None, and wonder what could cause this.

To answer some of the comments, the function does quite a lot. It includes things like graph searches and sending and receiving JSON data over a socket, so there are quite a few things that could go wrong. But the issue here is that the raised exception is None, which does not help my debugging at all.

Answer 1

Look at the type of the exception, I bet it's a KeyError:

try:
    dict()[None]
except Exception as e:
    print(type(e), e)

Output:

<class 'KeyError'> None

Answer 2

You're better off printing the repr of the exception, not the default str that print applies, eg:

from __future__ import print_function

try:
    run_arbitrary_code()
except Exception as e:
    print(repr(e))