CODEWITHSUNDEEP
pythonlistdictionary
Gyula Sámuel Karli
Gyula Sámuel Karli

Reputation: 3332

Python list of dicts: how to manipulate dynamically?

Is it possible to make a list of dicts such a way that when I change the dicts' content, the containing list reflects it (in spite of just storing in a copy of the original dict)?

a = {1: 1, 2, 2}
b = {3: 3, 4: 4}
c = [a, b]
c
[{1: 1, 2, 2}, {3: 3, 4: 4}]
a = {1: 6, 2: 7}
c
[{1: 1, 2, 2}, {3: 3, 4: 4}]

and not

[{1: 6, 2: 7}, {3: 3, 4: 4}]

(My goal is to have a 2D table-like structure that can be navigated both horizontally and vertically, and to avoid refreshing cols and rows after each new value entered in any cell. I need pointer-like behavior)

Upvotes: 0

Views: 153

Answers (3)

roman
roman

Reputation: 117380

When you do

a = {1: 6, 2: 7}

you just reassigning variable a, so it'll point to new dict, and variable c is not modified at all. Previous value of a is left only as first element of c.

So you have to either change element of c, like:

c[0] = {1: 6, 2: 7}

or change elements of a (but not reassign a):

a[1], a[2] = 6, 7

or

a.update({1:6, 2:7})

Upvotes: 1

arshajii
arshajii

Reputation: 129507

You can update a in-place using update() as opposed to reassigning it:

a.clear()
a.update({1: 6, 2: 7})

(See also: clear())

Using your full example:

>>> a = {1: 1, 2: 2}
>>> b = {3: 3, 4: 4}
>>> c = [a, b]
>>> c
[{1: 1, 2: 2}, {3: 3, 4: 4}]
>>> a.clear()
>>> a.update({1: 6, 2: 7})
>>> c
[{1: 6, 2: 7}, {3: 3, 4: 4}]  # <--

Upvotes: 2

Mark Ransom
Mark Ransom

Reputation: 308158

Instead of reassigning a you could modify it in place.

a[1] = 6
a[2] = 7

Upvotes: 0

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