How to Print Exception Stack Trace in Python

In Python, when an exception occurs, a stack trace provides details about the error, including the function call sequence, exact line and exception type. This helps in debugging and identifying issues quickly.

Key Elements of a Stack Trace:

• Traceback of the most recent call
• Location in the program
• Line where the error occurred
• Exception type and message

Let's explore different methods to achieve this.

Using traceback.print_exec()

traceback.print_exc() is a simple way to print the full exception stack trace directly to the console. It is useful when debugging code interactively or logging errors in basic scripts. It automatically captures the latest exception and prints its traceback without requiring extra parameters.

Example:

import traceback

try:
    1 / 0  # division by zero
except Exception:
    traceback.print_exc()

Output:

Traceback (most recent call last):
  File "/home/guest/sandbox/Solution.py", line 4, in <module>
    1 / 0  # division by zero
    ~~^~~
ZeroDivisionError: division by zero

Explanation: This code attempts to divide by zero inside a try block, which raises a ZeroDivisionError. The except block catches the exception and prints the detailed error traceback using traceback.print_exc(), helping in debugging by displaying where the error occurred.

Using traceback.format_exc()

traceback.format_exc() captures the stack trace as a string, making it useful for logging or displaying errors in custom formats. Instead of printing directly, it allows further processing, such as storing errors in logs or sending them in reports. This method provides flexibility while maintaining detailed traceback information.

Example:

import traceback

try:
    1 / 0  # division by zero
except Exception:
    error_msg = traceback.format_exc()
    print(error_msg)

Output:

Traceback (most recent call last):
  File "/home/guest/sandbox/Solution.py", line 4, in <module>
    1 / 0  # division by zero
    ~~^~~
ZeroDivisionError: division by zero

Explanation: The except block catches the exception and uses traceback.format_exc() to capture the complete error traceback as a string. This error message is then stored in error_msg and printed, providing detailed debugging information about where the error occurred.

Using logging module

logging module's logging.exception() method logs the error message along with the full stack trace, making it ideal for production environments. It ensures structured error logging with different severity levels and supports writing errors to log files, making debugging and monitoring easier.

Example:

import logging

logging.basicConfig(level=logging.ERROR)  # Set logging level

try:
    1 / 0  # division by zero
except Exception:
    logging.exception("An error occurred:")

Output:

ERROR:root:An error occurred:
Traceback (most recent call last):
  File "/home/guest/sandbox/Solution.py", line 6, in <module>
    1 / 0  # division by zero
    ~~^~~
ZeroDivisionError: division by zero

Explanation: except block catches the exception and uses logging.exception() to log the error message along with the complete traceback. The logging.basicConfig(level=logging.ERROR) sets the logging level to ERROR, ensuring that only error messages and above are logged.

Using sys.exc_info()

sys.exc_info() provides detailed control over exception handling by returning a tuple containing the exception type, value and traceback. It is useful for advanced debugging, custom error handling, or re-raising exceptions while maintaining full traceback details.

Example:

import sys
import traceback

try:
    1 / 0  # division by zero
except Exception:
    exc_type, exc_val, exc_tb = sys.exc_info()
    traceback.print_exception(exc_type, exc_val, exc_tb)

Output:

Traceback (most recent call last):
  File "/home/guest/sandbox/Solution.py", line 5, in <module>
    1 / 0  # division by zero
    ~~^~~
ZeroDivisionError: division by zero

Explanation: except block catches the exception and retrieves detailed exception information using sys.exc_info(), which returns a tuple containing the exception type, value and traceback object. These details are then passed to traceback.print_exception(), which prints the full error traceback.