[Tutor] I need to ignore an error let the script continue to run

[Jim]

On 5/5/20 4:13 PM, Mark Lawrence wrote:
> On 05/05/2020 21:28, Jim wrote:
>> On 5/5/20 9:38 AM, Jim wrote:
>>> On 5/5/20 3:01 AM, Alan Gauld via Tutor wrote:
>>>> On 05/05/2020 03:41, Jim wrote:
>>>>
>>>>> It seems try/except will not process the keys after the missing one.
>>>>
>>>> You need to wrap each bit that needs to continue in try/except.
>>>> Clunky I agree.
>>>>
>>>>> 'Recepient username: ' + header['to'].addresses[0].username+'\n',
>>>>> 'Sender name: ' + header['from'].addresses[0].display_name
>>>>>
>>>>> They don't look like keys, but they do resolve to the info I want 
>>>>> if it
>>>>> is in the header.
>>>>
>>>> They aren't keys they are accessing attributes of some class that is
>>>> returned. You could check the return value from header first using 
>>>> an if
>>>> test. Or you could just wrap those two calls in their own try/except.
>>>>
>>>> Or you could use get() and return a dummy instance of whatever class it
>>>> is with whatever default values you need.
>>>>
>>>> So several solutions only you can decide which suits you best.
>>>
>>> OK, thanks, I'll give them a try and see which on works best.
>>>
>>
>> It seems every time I tried to test the return value from header I 
>> would get an error, so I went the try/except route. This what I ended 
>> up with:
>>
>> def parse_header(msg):
>>      with open('/home/jfb/' + email_msg, 'rb') as fp:
>>          header = BytesHeaderParser(policy=default).parse(fp)
>>          #  Now the header items can be accessed as a dictionary:
>>          try:
>>              username =  header['to'].addresses[0].username + '\n'
>>          except:
> 
> Never use a bare except as in the long term it's asking for trouble, 
> catch what you know can occur and let anything else raise it's own 
> exception.
> 
>>              username = ' Blank \n'

I just write small scripts for my own use, so I really haven't had the 
occasion to use try/except much. I'm sure your advice it correct in most 
cases. I'm using try/except more like an 'if'. I needed some way to test 
if certain items were  not in the header data being returned. It seemed 
that no matter how I tried to reference them I got an error because they 
tried to return data that was not there. Maybe it can be done but I 
could never figure it out. Alan suggested a couple of things, one of 
which was try/except. That's how I came up with what you see. I'm 
probably abusing try/except, but it works and if it breaks I'll just 
have to fix it.

Thanks for your input.

Jim

>>          try:
>>              sender =  header['to'].addresses[0].display_name + '\n'
>>          except:
>>              sender = ' Blank \n'
>>
>>          return ['To: ' + header['to']+'\n' ,
>>          'From: ' + header['from']+'\n',
>>          'Subject: ' + header['subject']+'\n',
>>          'Return-Path: ' + header['return-path']+'\n' ,
>>          #These do not exist in some headers'
>>          'Recepient username: ' + username,
>>          'Sender name: ' + sender,
>>          ]
>> This works when every thing is in the header and when the last two are 
>> missing, so thanks for your help.
>>
>> Regards,  Jim
>>
> 
> 
>