Python: get value from dictionary when key is a list

Question

I have a dictionary where the key is a list

cfn = {('A', 'B'): 1, ('A','C'): 2 , ('A', 'D'): 3}
genes = ['A', 'C', 'D', 'E']

I am trying to get a value from the dictionary if the gene pairs in the key exist in a list together. My attempt is as follows, however I get TypeError: unhashable type: 'list'

def create_networks(genes, cfn):
    network = list()
    for i in range(0, len(genes)):
        for j in range(1, len(genes)):
            edge = cfn.get([genes[i], genes[j]],0)
            if edge > 0:
                network.append([genes[i], genes[j], edge])

desired output:

network = [['A','C', 2], ['A', 'D', 3]]

solution based on comments and answer below: edge = cfn.get((genes[i], genes[j]),0)

Asked By: keenan

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Source

Answer 1

Your keys in cfn are of type tuple as a key needs to be a hashable type.

Hashable types are immutable data types such as:

int
string
tuple
frozenset

as they can’t be changed or mutated. Otherwise you can’t access the value stored at that key.

So in your case you just need to change these [] into this ():

def create_networks(genes, cfn):
    network = list()
    for i in range(0, len(genes)):
        for j in range(1, len(genes)):
            # Use () to create a tuple
            edge = cfn.get((genes[i], genes[j]),0)
            if edge > 0:
                network.append([genes[i], genes[j], edge])
    return network

That way you don’t get the error and get your expected result of

>>> create_networks(genes, cfn)
[['A', 'C', 2], ['A', 'D', 3]]

Answered By: Wolric

Answer 2

You can do something like so:
https://onecompiler.com/python2/3yp8xepzp

cfn = {'AB': 1, 'AC': 2 , 'AD': 3}
genes = ['A', 'C', 'D', 'E']

def create_networks(genes, cfn):
    network = []
    for i in range(0, len(genes)):
        for j in range(1, len(genes)):
          keyy = genes[i]+''+genes[j]
          if keyy in cfn.keys():
            edge2 = cfn[genes[i]+''+genes[j]]
            if edge2 > 0:
                network.append([genes[i], genes[j], edge2])
    return network

print(create_networks(genes,cfn))

Answered By: Tirth

Python: get value from dictionary when key is a list

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