Problem statement :-
Whenever, we try to fetch the value against a key, our use case is that is the key doesn't exist in the dictionary then a list with only that key should be returned as the default value.
Below is an example :-
>>> dic = defaultdict(<function 'custom_default_function'>, {1: [1,2,6], 3: [3,6,8]})
>>> print(dic[1])
[1,2,6]
>>> print(dic[5])
[5]
In case of key with value 1
the output is completely fine as the key is there in dic.
But for the case when we trying to look for key 5
then the default value that the code must print should be [5]
i.e a list with only key as an element inside it.
I tried to write a default function but amm not getting on how to pass parameter to the default function.
def default_function(key):
return key
# Defining the dict
d = defaultdict(default_function)
d[1] = [1,4]
d[2] = [2,3]
print(d[4]) -> This will throw error as the positional argument for default_function is not missing
Could anyone please help me with what am I doing wrong and how can I resolve this using defaultdict in python.
CodePudding user response:
defaultdict
will not generate a new value that depends on the key...
you could inherit from dict
and overload __missing__
:
class MyDict(dict):
def __init__(self):
super().__init__()
def __missing__(self, key):
self[key] = [key]
return self[key]
my_dict = MyDict()
print(my_dict[5]) # -> [5]
print(my_dict) # -> {5: [5]}
there are 2 other answers here that might help: