Python: find closest key in a dictionary from the given input key

Question

I have a data in form a dictionary.. NOw I take the input from the user and it can be anything.. And I am trying to do the following. If the key exists then cool.. fetch the

Answer 1

Rather than using OrderedDict and bisect, consider the SortedDict type in the sortedcontainers module. It's a pure-Python and fast-as-C implementation of sorted list, sorted dict, and sorted set types with 100% testing coverage and hours of stress.

With a SortedDict you can bisect for the desired key. For example:

from itertools import islice
from sortedcontainers import SortedDict

def closest(sorted_dict, key):
    "Return closest key in `sorted_dict` to given `key`."
    assert len(sorted_dict) > 0
    keys = list(islice(sorted_dict.irange(minimum=key), 1))
    keys.extend(islice(sorted_dict.irange(maximum=key, reverse=True), 1))
    return min(keys, key=lambda k: abs(key - k))

The closest function uses SortedDict.irange to create an iterator of keys nearest the given key. The keys are bisected with log(N) runtime complexity.

>>> sd = SortedDict({-3: 'a', 0: 'b', 2: 'c'})
>>> for num in range(-5, 5):
...     key = closest(sd, num)
...     print('Given', num, ', closest:', key)
Given -5 , closest: -3
Given -4 , closest: -3
Given -3 , closest: -3
Given -2 , closest: -3
Given -1 , closest: 0
Given 0 , closest: 0
Given 1 , closest: 2
Given 2 , closest: 2
Given 3 , closest: 2
Given 4 , closest: 2

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