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key not found in dictionary

I have a dictionary and sometime the lookup fails...
it seems to raise an exception when this happens.
What should I do to fix/catch this problem?

desc = self.numericDict[k][2]
KeyError: 589824 <---- This is the error that is being produced,
because there is no key
589824.

Aug 22 '06 #1
9 5935

KraftDiner wrote:
I have a dictionary and sometime the lookup fails...
it seems to raise an exception when this happens.
What should I do to fix/catch this problem?

desc = self.numericDict[k][2]
KeyError: 589824 <---- This is the error that is being produced,
because there is no key
589824.
It raises a KeyError, as you are seeing. Just use a try/except
construction and handle the error as required by your application:

try:
desc = self.numericDict[k][2]
except KeyError, ke:
<do something - report the error to the user? ignore the error?>

Aug 22 '06 #2
KraftDiner wrote:
I have a dictionary and sometime the lookup fails...
it seems to raise an exception when this happens.
What should I do to fix/catch this problem?

desc = self.numericDict[k][2]
KeyError: 589824 <---- This is the error that is being produced,
because there is no key
589824.
Given the information provided the simplest answer would be:

try:
desc = self.numericDict[k][2]
except KeyError:
desc = ''

Aug 22 '06 #3
KraftDiner wrote:
I have a dictionary and sometime the lookup fails...
it seems to raise an exception when this happens.
What should I do to fix/catch this problem?

desc = self.numericDict[k][2]
KeyError: 589824 <---- This is the error that is being produced,
because there is no key
589824.
As stated you can wrap the access in the try - except - else statement,
as in

try:
foo['bar']
except :
# Handle the error.
pass
else :
# We have it, so use it...
print foo['bar']

Or you can use the has_key() and test it first. For example

if foo.has_key('bar'):
print 'we have it'
else :
print 'we don't have bar.'

That'll do it for me.

Chaz.
Aug 22 '06 #4
KraftDiner wrote:
I have a dictionary and sometime the lookup fails...
it seems to raise an exception when this happens.
What should I do to fix/catch this problem?

desc = self.numericDict[k][2]
KeyError: 589824 <---- This is the error that is being produced,
because there is no key
589824.
If you agree that the key is not there, then just catch the exception
(try ... except)

Philippe

Aug 22 '06 #5
Depending on what you want to do if the key doesn't exist, you might
want to use the dictionary method get() :

value = some_dict.get(key,default)

sets value to some_dict[key] if the key exists, and to default
otherwise

Regards,
Pierre

Aug 22 '06 #6
"KraftDiner" <bo*******@yahoo.comwrites:
I have a dictionary and sometime the lookup fails...
it seems to raise an exception when this happens.
What should I do to fix/catch this problem?

desc = self.numericDict[k][2]
KeyError: 589824 <---- This is the error that is being produced,
because there is no key
589824.
Others have suggested the general solution of using 'try ... except
Foo' for catching a particular exception and dealing with it.

In the specific use case of wanting a default value when a dictionary
doesn't have a particular key, you can also use this:
>>foo = {0: "spam", 1: "eggs", 7: "beans"}
for key in [1, 2, 7]:
... desc = foo.get(key, None)
... print repr(desc)
...
'eggs'
None
'beans'

A brief description is at 'help(dict.get)'.

--
\ "The illiterate of the future will not be the person who cannot |
`\ read. It will be the person who does not know how to learn." |
_o__) -- Alvin Toffler |
Ben Finney

Aug 23 '06 #7
Or you can use the has_key() and test it first. For example
>
if foo.has_key('bar'):
print 'we have it'
else :
print 'we don't have bar.'
Nowadays you can also say:

if 'bar' in foo:
# do something

Aug 23 '06 #8
Ben Finney wrote:
In the specific use case of wanting a default value when a dictionary
doesn't have a particular key, you can also use this:
>>foo = {0: "spam", 1: "eggs", 7: "beans"}
>>for key in [1, 2, 7]:
... desc = foo.get(key, None)
usually spelled

desc = foo.get(key) # returns None if not present

or

desc = foo.get(key, default)

if you want something other than None.

</F>

Aug 23 '06 #9
Chaz Ginger <cg********@hotmail.comwrote:
>KraftDiner wrote:
> desc = self.numericDict[k][2]
KeyError: 589824 <---- This is the error that is being produced,
As stated you can wrap the access in the try - except - else statement,
as in

try:
foo['bar']
except :
# Handle the error.
Bare "except" is generally a bad idea. Here, it could be letting
through whole truckloads of other errors. Suppose the OP typos:

try:
desc = self.numericDict[j][2]
except:
# handle missing key

but the except isn't handling a KeyError, it's got a NameError
(assuming j doesn't exist). Or what if self.numericDict[k] exists
but self.numericDict[k][2] gives a TypeError or IndexError? It
really needs to be:

except KeyError:

--
\S -- si***@chiark.greenend.org.uk -- http://www.chaos.org.uk/~sion/
___ | "Frankly I have no feelings towards penguins one way or the other"
\X/ | -- Arthur C. Clarke
her nu becomež se bera eadward ofdun hlęddre heafdes bęce bump bump bump
Aug 23 '06 #10

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