Catch KeyError in Python

Question

If I run the code   connection   manager connect  I2Cx     The program crashes and reports a KeyError because I2Cx doesn t exist  it should be I2C    But if I do   try      connection   manager connect  I2Cx   except Exception  e      print e   It doesn t print anything for e  I would like to be able to print the exception that was thrown  If I try the same thing with a divide by zero operation it is caught and reported properly in both cases  What am I missing here

User · Answer

I dont think python has a catch     try      connection   manager connect  I2Cx   except Exception  e      print e

User · Answer

If it s raising a KeyError with no message  then it won t print anything  If you do     try      connection   manager connect  I2Cx   except Exception as e      print repr e       you ll at least get the exception class name   A better alternative is to use multiple except blocks  and only  catch  the exceptions you intend to handle     try      connection   manager connect  I2Cx   except KeyError as e      print  I got a KeyError - reason   s     str e  except IndexError as e      print  I got an IndexError - reason   s     str e    There are valid reasons to catch all exceptions  but you should almost always re-raise them if you do     try      connection   manager connect  I2Cx   except KeyError as e      print  I got a KeyError - reason   s     str e  except      print  I got another exception  but I should re-raise      raise      because you probably don t want to handle KeyboardInterrupt if the user presses CTRL-C  nor SystemExit if the try-block calls sys exit

User · Answer

You should consult the documentation of whatever library is throwing the exception  to see how to get an error message out of its exceptions   Alternatively  a good way to debug this kind of thing is to say   except Exception  e      print dir e    to see what properties e has - you ll probably find it has a message property or similar

User · Answer

If you don t want to handle error just NoneType and use get   e g    manager connect get

User · Answer

Try print e message  this should be able to print your exception   try      connection   manager connect  I2Cx   except Exception  e      print e message

User · Answer

You can also try to use get    for example   connection   manager connect get  I2Cx     which won t raise a KeyError in case the key doesn t exist   You may also use second argument to specify the default value  if the key is not present

User · Answer

I am using Python 3 6 and using a comma between Exception and e does not work  I need to use the following syntax  just for anyone wondering   try      connection   manager connect  I2Cx   except KeyError as e      print e message

[python] Catch KeyError in Python

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