e.printStackTrace equivalent in python

e.printStackTrace equivalent in python

In Java, this does the following (docs):

public void printStackTrace()

Prints this throwable and its backtrace to the standard error stream...

This is used like this:

try
{ 
// code that may raise an error
}
catch (IOException e)
{
// exception handling
e.printStackTrace();
}

In Java, the Standard Error stream is unbuffered so that output arrives immediately.

The same semantics in Python 2 are:

import traceback
import sys
try: # code that may raise an error
    pass 
except IOError as e: # exception handling
    # in Python 2, stderr is also unbuffered
    print >> sys.stderr, traceback.format_exc()
    # in Python 2, you can also from __future__ import print_function
    print(traceback.format_exc(), file=sys.stderr)
    # or as the top answer here demonstrates, use:
    traceback.print_exc()
    # which also uses stderr.

Python 3

In Python 3, we can get the traceback directly from the exception object (which likely behaves better for threaded code). Also, stderr is line-buffered, but the print function gets a flush argument, so this would be immediately printed to stderr:

    print(traceback.format_exception(None, # <- type(e) by docs, but ignored 
                                     e, e.__traceback__),
          file=sys.stderr, flush=True)

Conclusion:

In Python 3, therefore, traceback.print_exc(), although it uses sys.stderr by default, would buffer the output, and you may possibly lose it. So to get as equivalent semantics as possible, in Python 3, use print with flush=True.

There is also logging.exception.

import logging

...

try:
    g()
except Exception as ex:
    logging.exception("Something awful happened!")
    # will print this message followed by traceback

Output:

ERROR 2007-09-18 23:30:19,913 error 1294 Something awful happened!
Traceback (most recent call last):
  File "b.py", line 22, in f
    g()
  File "b.py", line 14, in g
    1/0
ZeroDivisionError: integer division or modulo by zero

(From http://blog.tplus1.com/index.php/2007/09/28/the-python-logging-module-is-much-better-than-print-statements/ via How to print the full traceback without halting the program?)

import traceback
traceback.print_exc()

When doing this inside an except ...: block it will automatically use the current exception. See http://docs.python.org/library/traceback.html for more information.