How to Get Exception Information (Type, File, Line Number) in Python

Learn how to extract Python exception details like type, filename, and line number using exception objects, sys.exc_info(), and the traceback module for debugging.

When an exception occurs in Python, it's often crucial to get detailed information about it: the exception type, the file where it occurred, and the line number.

This guide explains how to retrieve this information using:

Attributes of the exception object itself.
The sys.exc_info() function.
The traceback module.

We'll cover single exceptions and how to handle multiple exceptions in a traceback.

Getting Exception Information from the Exception Object

The exception object itself (the e in except Exception as e:) contains valuable information:

try:
    raise ValueError('invalid value')
except ValueError as e:                                     # Catch the exception
    e_type = type(e).__name__                               # Get the exception type (e.g., 'ValueError')
    e_file = e.__traceback__.tb_frame.f_code.co_filename    # Get the filename
    e_line = e.__traceback__.tb_lineno                      # Get the line number
    e_message = str(e)                                      # Get the exception message

    print(f'exception type: {e_type}')                      # Output: exception type: ValueError
    print(f'exception filename: {e_file}')                  # Output: exception filename: /path/to/your/file.py
    print(f'exception line number: {e_line}')               # Output: exception line number: 2
    print(f'exception message: {e_message}')                # Output: exception message: invalid value

type(e).__name__: Gets the name of the exception class (e.g., "ValueError", "TypeError"). This is generally more reliable than using e.__class__.__name__ directly.
e.__traceback__: This is the traceback object associated with the exception. Traceback objects contain the call stack information.
e.__traceback__.tb_frame.f_code.co_filename: This drills down into the traceback to get the filename. tb_frame is the current stack frame, f_code is the code object, and co_filename is the filename.
e.__traceback__.tb_lineno: This gets the line number within the file where the exception occurred.
str(e): This gets the exception's message (the string argument you passed to raise ValueError(...)).

Getting Exception Information with `sys.exc_info()`

The sys.exc_info() function returns a tuple containing information about the currently handled exception:

import sys
import os

try:
    raise ValueError('invalid value')
except ValueError as e:
    e_type, e_object, e_traceback = sys.exc_info() # Get exception info

    e_filename = os.path.split(e_traceback.tb_frame.f_code.co_filename)[1] # Extract filename
    e_message = str(e)
    e_line_number = e_traceback.tb_lineno

    print(f'exception type: {e_type}')                  # Output: exception type: <class 'ValueError'>
    print(f'exception filename: {e_filename}')          # Output: exception filename: main.py
    print(f'exception line number: {e_line_number}')    # Output: exception line number: 5
    print(f'exception message: {e_message}')            # Output: exception message: invalid value

The method returns a tuple containing exception type, exception object, and exception traceback.

Getting Formatted Exception Information with `traceback`

The traceback module provides functions for working with tracebacks in a more structured way.

Using `traceback.format_exc()`

traceback.format_exc() returns a formatted string representing the entire traceback, similar to what you see when an unhandled exception occurs:

import traceback

try:
    raise ValueError('invalid value')
except ValueError as e:
    print(traceback.format_exc())

Output:

Traceback (most recent call last):
  File "/path/to/your/file.py", line 4, in <module>
    raise ValueError('invalid value')
ValueError: invalid value

Using `traceback.print_exc()`

traceback.print_exc() prints the formatted traceback directly to the console (or to a file if you specify one):

import traceback

try:
    raise ValueError('invalid value')
except ValueError as e:
    traceback.print_exc()

Output (to console):

Traceback (most recent call last):
  File "/path/to/your/file.py", line 4, in <module>
    raise ValueError('invalid value')
ValueError: invalid value

Handling Multiple Exceptions in a Traceback

If you have nested exceptions (an exception raised while handling another exception), you can iterate through the traceback to get information about each exception in the chain:

import sys
import os
try:
    raise ValueError('invalid value')
except ValueError as e:
    all_exceptions = []
    tback = e.__traceback__
    while tback is not None: # Iterate over the traceback frames
        e_type = type(e).__name__
        e_file = tback.tb_frame.f_code.co_filename
        e_line = tback.tb_lineno
        e_message = str(e)
        all_exceptions.append({
            'e_type': e_type,
            'e_file': e_file,
            'e_line': e_line,
            'e_message': e_message,
        })

        tback = tback.tb_next # Move to the *next* frame in the traceback
    print(all_exceptions)