Search of Dictionary Keys python

Question

I want to know how I could perform some kind of index on keys from a python dictionary. The dictionary holds approx. 400,000 items, so I am trying to avoid a linear search.

Answer 1

You could join all the keys into one long string with a suitable separator character and use the find method of the string. That is pretty fast.

Perhaps this code is helpful to you. The search method returns a list of dictionary values whose keys contain the substring key.

class DictLookupBySubstr(object):
    def __init__(self, dictionary, separator='\n'):
        self.dic = dictionary
        self.sep = separator
        self.txt = separator.join(dictionary.keys())+separator

    def search(self, key):
        res = []
        i = self.txt.find(key)
        while i >= 0:
            left = self.txt.rfind(self.sep, 0, i) + 1
            right = self.txt.find(self.sep, i)
            dic_key = self.txt[left:right]
            res.append(self.dic[dic_key])
            i = self.txt.find(key, right+1)
        return res