Question

import os, sys
from cStringIO import StringIO
import traceback

old_stdErr = sys.stderr
sys.stderr = mystdErr = StringIO()

try:
    p = 100/0
except Exception:
     traceback.print_exc(file=sys.stderr)

print mystdErr.getvalue()             ### -- 1st Print statement 

try:
   q = 100/0
except Exception:
   traceback.print_exc(file = sys.stderr)

print mystdErr.getvalue()             ### -- 2nd Print statement

This piece of code .. What the output will be

Output from the 1st print statement

Traceback (most recent call last):
File “C:\Users\manojtut\Desktop\untitled-1.py”, line 9, in
p = 100/0
ZeroDivisionError: integer division or modulo by zero

Output from the 2nd print statement

Traceback (most recent call last):
File “C:\Users\manojtut\Desktop\untitled-1.py”, line 9, in
p = 100/0
ZeroDivisionError: integer division or modulo by zero
Traceback (most recent call last):
File “C:\Users\manojtut\Desktop\untitled-1.py”, line 16, in
q = 100/0
ZeroDivisionError: integer division or modulo by zero

As you can see , the exception encountered at 1st zerodivision is being printed again in the second print statement which I don’t want. Can I somehow eliminate/flush away the first exception traceback so that only the second exception’s traceback can be printed in the second print statement?

Answer 1

Add this:

mystdErr.reset()
mystdErr.truncate()

before the second block. reset resets the file position to the beginning and writing begins from there. truncate removes all data after the current position. If ‘truncate’ is omitted – the data in the stream will be overwritten from subsequent writes.