CODEWITHSUNDEEP
pythondictionaryappend
Chris
Chris

Reputation: 1219

Python dictionary append to key?

I have been doing some reading and I think the correct solution to what I am trying to achieve is a dictionary...

I have been playing and looking at examples and they seem the way to go. I am having a problem though. While I can create a key and set its value without issues, I am unable to add values to an existing key.

Here is what I am trying

dict = {}
...
if key not in dict:
   dict[key] = value
else:
   dict[key].append(value)

It gives me...

AttributeError: 'str' object has no attribute 'append'

The if else statement is firing correctly if I use prints. The key is added if it does not exist. The error only occurs on the append line.

What I expect is a list of values per key.

Thanks, Chris

Upvotes: 1

Views: 87

Answers (2)

ClimateUnboxed
ClimateUnboxed

Reputation: 8077

I think you just need to insert your initial key as a list with one element:

dict = {}
...
if key not in dict:
   dict[key]=[value]
else:
   dict[key].append(value)

this works fine:

dict={}
dict["key"]=[1]
dict["key"].append(2)
dict 

{'key': [1, 2]}

Upvotes: 1

dbokers
dbokers

Reputation: 920

As mentioned by @kenny

All you have to do is

from collections import defaultdict

dic = defaultdict(list)

# it creates a list if the key is not in dictionary automatically
dic[key].append(value)

Upvotes: 2

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