Handling multiple KeyErrors in Python

Question

I get this error when I try to catch a KeyError twice. Is there anything in python which prevents you trying to catch the same error twice?

$ ./scratch.py
try getting a
can't get a try getting b
Traceback (most recent call last):
  File "./scratch.py", line 13, in <module>
    print dict['b']
KeyError: 'b'

The simplified code is below

dict={}
dict['c'] = '3'

try:
        print 'try getting a'
        print dict['a']
except KeyError:
        print 'can\'t get a try getting b'
        print dict['b']
except:
        print 'can\'t get a or b'

why not use dict.get? you also don't have the print dict['b'] in a try. — Padraic Cunningham
– Padraic Cunningham, Commented Jul 24, 2014 at 10:34
Hi Padriac- dict.get doesn't seem to throw an exception and fails silently? I would like to do something if I can't get a key. — nev
– nev, Commented Jul 24, 2014 at 11:42

wim · Accepted Answer · 2014-07-24 12:53:39Z

2

I would do this with a simple for loop:

>>> d = {'c': 1}
>>> keys = ['a', 'b', 'c']
>>> for key in keys:
...     try:
...         value = d[key]
...         break
...     except KeyError:
...         pass
... else:
...     raise KeyError('not any of keys in dict')
... 
>>> value
1
>>> key
'c'

If you want to do it in one line:

key, value = next((k, d[k]) for k in keys if k in d)

edited Jul 24, 2014 at 12:53

answered Jul 24, 2014 at 12:47

wim

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Comments

Anthony Kong · Accepted Answer · 2014-07-24 10:33:52Z

0

You need an extra try...except:

dict={}
dict['c'] = '3'

try:
        print 'try getting a'
        print dict['a']
except KeyError:
        print 'can\'t get a try getting b'
        try:
            print dict['b']
        except KeyError as e:
            print "Got another exception", e
except:
        print 'can\'t get a or b'

answered Jul 24, 2014 at 10:33

Anthony Kong

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2 Comments

Kasisnu Over a year ago

I don't think the indent is right for the second try, logically. Because if dict['a'] exists, there is no error and it never tries to check for dict['b']

Anthony Kong Over a year ago

I believe @nev is using the code snippet to understand the python exception handling mechanism. The key point I want to make is: if you want to handle an exception thrown within an exception handler, you need to add another try...except block. Here is a similar question in OS: stackoverflow.com/questions/17015230/…

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