Retrieving the value of a key by the hash of the key in Python

Question

I have the below dictionary:

>>> dict1={'a':1,'b':2}
>>>
>>>
>>> dict1['a']
1
>>>

Q: Is there a way to retrieve the value of key (in the above dictionary), using the hash value of the key? If I print 'a'.__hash__ , I get:

>>> print 'a'.__hash__
<method-wrapper '__hash__' of str object at 0x00000000021AA0F8>
>>>

Q2: Why not do a key lookup directly rather than converting the key to a hash value and then do the lookup? I read that using hash makes it faster.

There is not necessary a one-to-one mapping between the hash and the key, it depends on the implementation and on the key. Of course Python manages to do the lookup, and I suggest you download the C source and read Objects/dictnotes.txt and Objects/dictobject.c. Then you will probably decide it is better to let Python do it. — cdarke
– cdarke, Commented Feb 1, 2017 at 9:08

gzc · Accepted Answer · 2017-02-01 07:51:38Z

2

You don't need to retrieve the value using hash by yourself, Python dict do that for you. Python dict use hash internally.

from https://docs.python.org/3/library/stdtypes.html#typesmapping

A mapping object maps hashable values to arbitrary objects. Mappings are mutable objects. There is currently only one standard mapping type, the dictionary.

edited Feb 1, 2017 at 7:51

answered Feb 1, 2017 at 7:38

gzc

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1 Comment

fsociety Over a year ago

i understand what you say, but i need to know if there is a way to get the value of a key(in a dict) using the hash of the key ?

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