[Tutor] How to control the not existent keys in a dict

[Richard Lovely]

2009/5/10 Emilio Casbas <ecasbasj at yahoo.es>:
>
> Hello,
>
> I have some problems testing keys not existent in a dictionary.
> The code works testing existent keys with his corresponding value, but
> If I enter a not existent key, an exception is raised.
> How can I control the not existent key and assign him a default value?
>
> user at cipher:~/project/programming/python$ python3.0 test.py
> ¿What is your name? KEY-NOT-EXISTENT
> Good Morning KEY-NOT-EXISTENT
> ¿Which is the secret word? any
> Traceback (most recent call last):
>  File "test.py", line 30, in <module>
>    while not correct_password(name,guess,dictionary):
>  File "test.py", line 8, in correct_password
>    if (is_in_dict and password == dict[nombre.capitalize()]):
> KeyError: 'KEY-NOT-EXISTENT'
>
> -relevant code snippet-
> dictionary = {'Mark': 'python', 'Dave': 'java', 'Ane': 'C++', 'default':'pass'}
>
> def correct_password(name,password,dict):
>        if (not is_in_dict and password == dict['default']):
>                return 1
>        elif (is_in_dict and password == dict[nombre.capitalize()]):
>                return 1
>        return 0
>
> def is_in_dict(nom,dict):
>        for n in dict:
>                if nom.lower() == n.lower():
>                        return 1
>        return 0
> -end relevant code snippet-
>
> Regards
>
>
>
>
> _______________________________________________
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> http://mail.python.org/mailman/listinfo/tutor
>

There's also collections.defaultdict, which you can initialise with a
"default value factory" which will generate a value for every attempt
to get a non-existent key.  It can be a lot of fun with a bit of
thought.


-- 
Richard "Roadie Rich" Lovely, part of the JNP|UK Famile
www.theJNP.com