python exception message capturing

Question

import ftplib import urllib2 import os import logging logger   logging getLogger  ftpuploader   hdlr   logging FileHandler  ftplog log   formatter   logging Formatter    asctime s   levelname s   message s   hdlr setFormatter formatter  logger addHandler hdlr  logger setLevel logging INFO  FTPADDR    some ftp address   def upload to ftp con  filepath       try          f   open filepath  rb                    file to send         con storbinary  STOR    filepath  f            Send the file         f close                                    Close file and FTP         logger info  File successfully uploaded to    FTPADDR      except  e          logger error  Failed to upload to ftp     str e     This doesn t seem to work  I get syntax error  what is the proper way of doing this for logging all kind of exceptions to a file

User · Answer

You can use logger exception  msg   for logging exception with traceback   try       your code except Exception as e      logger exception  Failed      str e

User · Answer

The syntax is no longer supported in python 3  Use the following instead   try      do something   except BaseException as e      logger error  Failed to do something      str e

User · Answer

If you want the error class  error message  and stack trace  use sys exc info    Minimal working code with some formatting  import sys import traceback  try      ans   1 0 except BaseException as ex        Get current system exception     ex type  ex value  ex traceback   sys exc info          Extract unformatter stack traces as tuples     trace back   traceback extract tb ex traceback         Format stacktrace     stack trace   list        for trace in trace back          stack trace append  quot File    s   Line    d  Func Name    s  Message    s quot     trace 0   trace 1   trace 2   trace 3         print  quot Exception type    s  quot    ex type   name        print  quot Exception message    s quot   ex value      print  quot Stack trace    s quot   stack trace   Which gives the following output  Exception type   ZeroDivisionError Exception message   division by zero Stack trace     File      test py   Line   5  Func Name    lt module gt   Message   ans   1 0    The function sys exc info   gives you details about the most recent exception  It returns a tuple of  type  value  traceback   traceback is an instance of traceback object  You can format the trace with the methods provided  More can be found in the traceback documentation

User · Answer

Updating this to something simpler for logger  works for both python 2 and 3   You do not need traceback module   import logging  logger   logging Logger  catch all    def catchEverythingInLog        try              do something         except Exception as e          logger error e  exc info True              exception handling       This is now the old way  though still works    import sys  traceback  def catchEverything        try              some operation s          except          exc type  exc value  exc traceback   sys exc info               exception handling       exc value is the error message

User · Answer

After python 3 6  you can use formatted string literal  It s neat   https   docs python org 3 whatsnew 3 6 html whatsnew36-pep498   try      except Exception as e      logger error f Failed to upload to ftp   e

User · Answer

You have to define which type of exception you want to catch  So write except Exception  e  instead of except  e  for a general exception  that will be logged anyway    Other possibility is to write your whole try except code this way   try      with open filepath  rb   as f          con storbinary  STOR    filepath  f      logger info  File successfully uploaded to    FTPADDR  except Exception  e    work on python 2 x     logger error  Failed to upload to ftp     str e     in Python 3 x and modern versions of Python 2 x use except Exception as e instead of except Exception  e   try      with open filepath  rb   as f          con storbinary  STOR    filepath  f      logger info  File successfully uploaded to    FTPADDR  except Exception as e    work on python 3 x     logger error  Failed to upload to ftp     str e

User · Answer

There are some cases where you can use the e message or e messages   But it does not work in all cases  Anyway the more safe is to use the str e    try        except Exception as e    print e message

User · Answer

Using str e  or repr e  to represent the exception  you won t get the actual stack trace  so it is not helpful to find where the exception is  After reading other answers and the logging package doc  the following two ways works great to print the actual stack trace for easier debugging  use logger debug   with parameter exc info try        my code except SomeError as e      logger debug e  exc info True   use logger exception   or we can directly use logger exception   to print the exception  try        my code except SomeError as e      logger exception e

User · Answer

for the future strugglers   in python 3 8 2 and maybe a few versions before that   the syntax is  except Attribute as e      print e

User · Answer

You can try specifying the BaseException type explicitly  However  this will only catch derivatives of BaseException  While this includes all implementation-provided exceptions  it is also possibly to raise arbitrary old-style classes   try    do something   except BaseException  e    logger error  Failed to do something      str e

User · Answer

Use str ex  to print execption  try      your code except ex     print str ex

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