# [Tutor] how to delete some quasi-duplicated keys

lina lina.lastname at gmail.com
Fri Nov 25 13:40:39 CET 2011

```On Fri, Nov 25, 2011 at 7:19 PM, Steven D'Aprano <steve at pearwood.info> wrote:
> lina wrote:
>>
>> On Fri, Nov 25, 2011 at 5:06 PM, Steven D'Aprano <steve at pearwood.info>
>> wrote:
>
>>> pair = frozenset(('66', '69'))
>>> pairs[pair] = pairs.get(pair, 0) + value
>>
>> I don't get this "pairs.get" part.
>
> The "get" method does a look-up on a dict, but instead of failing if the key
> is missing, it returns a default value:
>
> py> d = {'a': 2}
> py> d['b']  # fails
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> KeyError: 'b'
> py> d.get('b', 3)  # use 3 as the default
> 3
>
>
>>  pairs[pair]=pairs.get(pair,0)+parts[2]
>> TypeError: unsupported operand type(s) for +: 'int' and 'str'
>
> Lina, in your original example, the values of the dict are integers:
Ha ... it's me.
>
> {('66', '69'): 217, ('69', '66'): 75, ('64', '71'): 25}
>
> The error you show above can only happen if they are not integers, but
> strings. When you show us examples, please get the examples right. If you
> give us wrong information, how do you expect us to help?
Sorry, I was confused at that time.
>
> You should convert all the strings into ints.
>
>
>> or line in f.readlines():
>>            parts=line.split()
>>            #pair=set((parts[0],parts[1]))
>>            if (parts[0],parts[1]) not in dehydrons.keys():
>>                dehydrons[(parts[0],parts[1])]=parts[2]
>>                occurence[(parts[0],parts[1])]=1
>>                pair=frozenset(('parts[0]','parts[1]'))
>>                pairs[pair]=pairs.get(pair,0)+parts[2]
>>            else:
>>                occurence[(parts[0],parts[1])]+=1
>
>
> f = open("some file")
> dehydrons = {}
> occurrence = {}
> pairs = {}
> for line in f.readlines():
>    parts = line.split()
>    # convert to ints
>    parts = [int(s) for s in parts]
>    pair = frozenset(parts[:2])  # order doesn't matter
>    if pair in dehydrons:
>        occurrence[pair] += 1
>    else:
>        dehydrons[pair] = parts[2]
>        occurrence[pair] = 1
>        pairs[pair] = pairs.get(pair, 0) + parts[2]
> f.close()
>
for line in f.readlines():
parts = line.split()
#pair=set((parts[0],parts[1]))
#convert to ints
parts = [int(s) for s in parts]
pair = frozenset(parts[:2])
print(pair)
if pair in dehydrons:
occurence[pair] += 1
else:
dehydrons[pair] = parts[2]
pairs[pair] = pairs.get(pair,0) + parts[2]
print(pairs)

\$ python3 dehydron_data_frozenset_version.py
frozenset({2, 15})
frozenset({2, 15})
Traceback (most recent call last):
File "dehydron_data_frozenset_version.py", line 35, in <module>
occurence[pair] += 1
KeyError: frozenset({2, 15})

Thanks,

>
>
> --
> Steven
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
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>
```

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