First, do not use prints for logging, there is a stable, proven and well-thought out stdlib module to do that: logging. You definitely should use it instead.

Second, do not be tempted to do a mess with unrelated tools when there is a native and simple approach. Here it is:

log = logging.getLogger(__name__)

try:
    call_code_that_fails()
except MyError:
    log.exception('Any extra info you want to see in your logs')

That's it. You are done now.

Explanation for anyone who is interested in how things work under the hood

What log.exception is actually doing is just a call to log.error (that is, log event with level ERROR) and print traceback then.

Why is it better?

Well, here are some considerations:

• it is just right;
• it is straightforward;
• it is simple.

Why should nobody use traceback or call logger with exc_info=True or get their hands dirty with sys.exc_info?

Well, just because! They all exist for different purposes. For example, traceback.print_exc's output is a little bit different from tracebacks produced by the interpreter itself. If you use it, you will confuse anyone who reads your logs, they will be banging their heads against them.

Passing exc_info=True to log calls is just inappropriate. But, it is useful when catching recoverable errors and you want to log them (using, e.g INFO level) with tracebacks as well, because log.exception produces logs of only one level - ERROR.

And you definitely should avoid messing with sys.exc_info as much as you can. It's just not a public interface, it's an internal one - you can use it if you definitely know what you are doing. It is not intended for just printing exceptions.

traceback.format_exception(exception_object)

If you only have the exception object, you can get the traceback as a string from any point of the code in Python 3 with:

import traceback

''.join(traceback.format_exception(None, exc_obj, exc_obj.__traceback__))

Full example:

#!/usr/bin/env python3

import traceback

def f():
    g()

def g():
    raise Exception('asdf')

try:
    g()
except Exception as e:
    exc_obj = e

tb_str = ''.join(traceback.format_exception(None, exc_obj, exc_obj.__traceback__))
print(tb_str)

Output:

Traceback (most recent call last):
  File "./main.py", line 12, in <module>
    g()
  File "./main.py", line 9, in g
    raise Exception('asdf')
Exception: asdf

Documentation: https://docs.python.org/3.9/library/traceback.html#traceback.format_exception

See also: Extract traceback info from an exception object

Tested in Python 3.9

In addition to Aaron Hall's answer, if you are logging, but don't want to use logging.exception() (since it logs at the ERROR level), you can use a lower level and pass exc_info=True. e.g.

try:
    do_something_that_might_error()
except Exception:
    logging.info('General exception noted.', exc_info=True)

I don't see this mentioned in any of the other answers. If you're passing around an Exception object for whatever reason...

In Python 3.5+ you can get a trace from an Exception object using traceback.TracebackException.from_exception(). For example:

import traceback


def stack_lvl_3():
    raise Exception('a1', 'b2', 'c3')


def stack_lvl_2():
    try:
        stack_lvl_3()
    except Exception as e:
        # raise
        return e


def stack_lvl_1():
    e = stack_lvl_2()
    return e

e = stack_lvl_1()

tb1 = traceback.TracebackException.from_exception(e)
print(''.join(tb1.format()))

However, the above code results in:

Traceback (most recent call last):
  File "exc.py", line 10, in stack_lvl_2
    stack_lvl_3()
  File "exc.py", line 5, in stack_lvl_3
    raise Exception('a1', 'b2', 'c3')
Exception: ('a1', 'b2', 'c3')

This is just two levels of the stack, as opposed to what would have been printed on screen had the exception been raised in stack_lvl_2() and not intercepted (uncomment the # raise line).

As I understand it, that's because an exception records only the current level of the stack when it is raised, stack_lvl_3() in this case. As it's passed back up through the stack, more levels are being added to its __traceback__. But we intercepted it in stack_lvl_2(), meaning all it got to record was levels 3 and 2. To get the full trace as printed on stdout we'd have to catch it at the highest (lowest?) level:

import traceback


def stack_lvl_3():
    raise Exception('a1', 'b2', 'c3')


def stack_lvl_2():
    stack_lvl_3()


def stack_lvl_1():
    stack_lvl_2()


try:
    stack_lvl_1()
except Exception as exc:
    tb = traceback.TracebackException.from_exception(exc)

print('Handled at stack lvl 0')
print(''.join(tb.stack.format()))

Which results in:

Handled at stack lvl 0
  File "exc.py", line 17, in <module>
    stack_lvl_1()
  File "exc.py", line 13, in stack_lvl_1
    stack_lvl_2()
  File "exc.py", line 9, in stack_lvl_2
    stack_lvl_3()
  File "exc.py", line 5, in stack_lvl_3
    raise Exception('a1', 'b2', 'c3')

Notice that the stack print is different, the first and last lines are missing. Because it's a different format().

Intercepting the exception as far away from the point where it was raised as possible makes for simpler code while also giving more information.

In python3 (works in 3.9) we can define a function and can use that where ever we want to print the details.

import traceback

def get_traceback(e):
    lines = traceback.format_exception(type(e), e, e.__traceback__)
    return ''.join(lines)

try:
    1/0
except Exception as e:
    print('------Start--------')
    print(get_traceback(e))
    print('------End--------')

try:
    spam(1,2)
except Exception as e:
    print('------Start--------')
    print(get_traceback(e))
    print('------End--------')

The output would be like:

bash-3.2$ python3 /Users/soumyabratakole/PycharmProjects/pythonProject/main.py
------Start--------
Traceback (most recent call last):
  File "/Users/soumyabratakole/PycharmProjects/pythonProject/main.py", line 26, in <module>
    1/0
ZeroDivisionError: division by zero

------End--------
------Start--------
Traceback (most recent call last):
  File "/Users/soumyabratakole/PycharmProjects/pythonProject/main.py", line 33, in <module>
    spam(1,2)
NameError: name 'spam' is not defined

------End--------

If you have an Error object already, and you want to print the whole thing, you need to make this slightly awkward call:

import traceback
traceback.print_exception(type(err), err, err.__traceback__)

That's right, print_exception takes three positional arguments: The type of the exception, the actual exception object, and the exception's own internal traceback property.

In python 3.5 or later, the type(err) is optional... but it's a positional argument, so you still have to explicitly pass None in its place.

traceback.print_exception(None, err, err.__traceback__)

I have no idea why all of this isn't just traceback.print_exception(err). Why you would ever want to print out an error, along with a traceback other than the one that belongs to that error, is beyond me.

A remark about this answer's comments: print(traceback.format_exc()) does a better job for me than traceback.print_exc(). With the latter, the hello is sometimes strangely "mixed" with the traceback text, like if both want to write to stdout or stderr at the same time, producing weird output (at least when building from inside a text editor and viewing the output in the "Build results" panel).

Traceback (most recent call last):
File "C:\Users\User\Desktop\test.py", line 7, in
hell do_stuff()
File "C:\Users\User\Desktop\test.py", line 4, in do_stuff
1/0
ZeroDivisionError: integer division or modulo by zero
o
[Finished in 0.1s]

So I use:

import traceback, sys

def do_stuff():
    1/0

try:
    do_stuff()
except Exception:
    print(traceback.format_exc())
    print('hello')

import io
import traceback

try:
    call_code_that_fails()
except:

    errors = io.StringIO()
    traceback.print_exc(file=errors)
    contents = str(errors.getvalue())
    print(contents)
    errors.close()

This is my solution to write the error in a log file and also on console:

import logging, sys
import traceback
logging.basicConfig(filename='error.log', level=logging.DEBUG)

def handle_exception(exc_type, exc_value, exc_traceback):
    if issubclass(exc_type, KeyboardInterrupt):
        sys.__excepthook__(exc_type, exc_value, exc_traceback)
        return
    exc_info=(exc_type, exc_value, exc_traceback)
    logging.critical("\nDate:" + str(datetime.datetime.now()), exc_info=(exc_type, exc_value, exc_traceback))
    print("An error occured, check error.log to see the error details")
    traceback.print_exception(*exc_info)


sys.excepthook = handle_exception

python 3 solution

stacktrace_helper.py:

from linecache import getline
import sys
import traceback


def get_stack_trace():
    exc_type, exc_value, exc_tb = sys.exc_info()
    trace = traceback.format_stack()
    trace = list(filter(lambda x: ("\\lib\\" not in x and "/lib/" not in x and "stacktrace_helper.py" not in x), trace))
    ex_type = exc_type.__name__
    ex_line = exc_tb.tb_lineno
    ex_file = exc_tb.tb_frame.f_code.co_filename
    ex_message = str(exc_value)
    line_code = ""
    try:
        line_code = getline(ex_file, ex_line).strip()
    except:
        pass

    trace.insert(
        0, f'File "{ex_file}", line {ex_line}, line_code: {line_code} , ex: {ex_type} {ex_message}',
    )
    return trace


def get_stack_trace_str(msg: str = ""):
    trace = list(get_stack_trace())
    trace_str = "\n".join(list(map(str, trace)))
    trace_str = msg + "\n" + trace_str
    return trace_str

You could do:

try:
    do_stuff()
except Exception, err:
    print(Exception, err)
    raise err