I have the key of a python dictionary and I want to get the corresponding index in the dictionary. Suppose I have the following dictionary,
d = { 'a': 10, 'b': 20, 'c': 30}
Is there a combination of python functions so that I can get the index value of 1, given the key value 'b'?
d.??('b')
I know it can be achieved with a loop or lambda (with a loop embedded). Just thought there should be a more straightforward way.
This question is related to
python
python-2.7
dictionary
indexing
key
Dictionaries in python have no order. You could use a list of tuples as your data structure instead.
d = { 'a': 10, 'b': 20, 'c': 30}
newd = [('a',10), ('b',20), ('c',30)]
Then this code could be used to find the locations of keys with a specific value
locations = [i for i, t in enumerate(newd) if t[0]=='b']
>>> [1]
#Creating dictionary
animals = {"Cat" : "Pat", "Dog" : "Pat", "Tiger" : "Wild"}
#Convert dictionary to list (array)
keys = list(animals)
#Printing 1st dictionary key by index
print(keys[0])
#Done :)
No, there is no straightforward way because Python dictionaries do not have a set ordering.
From the documentation:
Keys and values are listed in an arbitrary order which is non-random, varies across Python implementations, and depends on the dictionary’s history of insertions and deletions.
In other words, the 'index' of b
depends entirely on what was inserted into and deleted from the mapping before:
>>> map={}
>>> map['b']=1
>>> map
{'b': 1}
>>> map['a']=1
>>> map
{'a': 1, 'b': 1}
>>> map['c']=1
>>> map
{'a': 1, 'c': 1, 'b': 1}
As of Python 2.7, you could use the collections.OrderedDict()
type instead, if insertion order is important to your application.
Source: Stackoverflow.com