"chaining" python exception

chained.py

import traceback
import sys


def a(x): b(x)

def b(x): c(x)

def c(x): d(x)

def d(x): raise Exception("blah %s" % x)

try:
  a(1)
except:
  orig_tb = traceback.format_exception(*sys.exc_info())[1:]
  raise Exception(''.join(["foo\n", "\tcaused by:\n"] + orig_tb))

## output:
Traceback (most recent call last):
  File "<stdin>", line 9, in <module>
Exception: foo
	caused by:
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 1, in a
  File "<stdin>", line 1, in b
  File "<stdin>", line 1, in c
  File "<stdin>", line 1, in d
Exception: blah 1