CODEWITHSUNDEEP
pythondictionary
Tarun K
Tarun K

Reputation: 499

Create multiple dictionaries in one line without reference to others?

I need to create multiple dictionaries in one line, I tried like following. 

a,b,c = dict(), dict(), dict()

Is there any pythonic way to achieve this? I tried with

a = b = c = dict()

But in this, if I change a it also reflects with other dicts

a['k'] = 'val'

a
{'k': 'val'}

b
{'k': 'val'}

c
{'k': 'val'}

Upvotes: 3

Views: 5972

Answers (2)

Aaditya Ura
Aaditya Ura

Reputation: 12669

Your first method is fine. use

a,b,c = dict(), dict(), dict()

The explanation for the second method :

Python variables are references to objects, but the actual data is contained in the objects.

a = b = c = dict() is not creating three dict. In python, variables don't store the value. Variables point to the object and objects store the value, so here a,b,c variable pointing same object which contains one dict(). you can check 

print(id(a),id(b),id(c))
4321042248 4321042248 4321042248

That's why when you change in one, it changes the other too because they are holding the same dict value.

Upvotes: 2

Anton vBR
Anton vBR

Reputation: 18906

I'm just posting some thoughts here:

Pep 8 is a style guide for python code: https://www.python.org/dev/peps/pep-0008/. However nothing about declaring variables there.

Although these work:

a,b,c = dict(), dict(), dict()
a, b, c = [dict() for _ in range(3)]

I think this is the most readable:

a = dict()
b = dict()
c = dict()

Reason:

You can always expect that variables are defined on separate rows. What about if you were to assign 20 items, would it be: a,b,c,d,e.... ??

Anyhow, another way of doing it would be to nest them inside one dictionary, and here too only one variable is declared:

dicts = {letter:dict() for letter in list("abc")} # {'a': {}, 'b': {}, 'c': {}}

Upvotes: 3

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