Difference between except and except Exception as e in Python

Question

Both the following snippets of code do the same thing  They catch every exception and execute the code in the except  block  Snippet 1 -   try       some code that may throw an exception except       exception handling code   Snippet 2 -   try       some code that may throw an exception except Exception as e       exception handling code   What is exactly the difference in both the constructs

User · Answer

There are differences with some exceptions, e.g. KeyboardInterrupt.

Reading PEP8:

A bare except: clause will catch SystemExit and KeyboardInterrupt exceptions, making it harder to interrupt a program with Control-C, and can disguise other problems. If you want to catch all exceptions that signal program errors, use except Exception: (bare except is equivalent to except BaseException:).

User · Answer

except    accepts all exceptions  whereas  except Exception as e    only accepts exceptions that you re meant to catch   Here s an example of one that you re not meant to catch    gt  gt  gt  try          input       except          pass       gt  gt  gt  try          input       except Exception as e          pass      Traceback  most recent call last     File   lt stdin gt    line 2  in  lt module gt  KeyboardInterrupt   The first one silenced the KeyboardInterrupt   Here s a quick list   issubclass BaseException  BaseException    gt  gt  gt  True issubclass BaseException  Exception    gt  gt  gt  False   issubclass KeyboardInterrupt  BaseException    gt  gt  gt  True issubclass KeyboardInterrupt  Exception    gt  gt  gt  False   issubclass SystemExit  BaseException    gt  gt  gt  True issubclass SystemExit  Exception    gt  gt  gt  False   If you want to catch any of those  it s best to do  except BaseException    to point out that you know what you re doing     All exceptions stem from BaseException  and those you re meant to catch day-to-day  those that ll be thrown for the programmer  inherit too from Exception

User · Answer

Another way to look at this  Check out the details of the exception  In  49   try                open  file DNE txt             except Exception as  e                print dir e                                                                                                                                                     cause        class        context        delattr        dict        dir        doc        eq        format        ge        getattribute        gt        hash        init        init subclass        le        lt        ne        new        reduce        reduce ex        repr        setattr        setstate        sizeof        str        subclasshook        suppress context        traceback      args    characters written    errno    filename    filename2    strerror    with traceback    There are lots of  quot things quot  to access using the  as e  syntax  This code was solely meant to show the details of this instance

User · Answer

Using the second form gives you a variable  named based upon the as clause  in your example e  in the except block scope with the exception object bound to it so you can use the infomration in the exception  type  message  stack trace  etc  to handle the exception in a more specially tailored manor

User · Answer

In the second you can access the attributes of the exception object    gt  gt  gt  def catch            try              asd           except Exception as e              print e message  e args       gt  gt  gt  catch   global name  asd  is not defined   global name  asd  is not defined      But it doesn t catch BaseException or the system-exiting exceptions SystemExit  KeyboardInterrupt and GeneratorExit    gt  gt  gt  def catch            try              raise BaseException           except Exception as e              print e message  e args       gt  gt  gt  catch   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 3  in catch BaseException   Which a bare except does    gt  gt  gt  def catch            try              raise BaseException           except              pass       gt  gt  gt  catch    gt  gt  gt     See the Built-in Exceptions section of the docs and the Errors and Exceptions section of the tutorial for more info

[python] Difference between except: and except Exception as e: in Python

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