I have the following situation:
>>> a = 1
>>> d = {"a": a}
>>> d
{'a': 1}
>>> d["a"] = 2
>>> d
{'a': 2}
>>> a
1
Of course this is the desired behaviour. However, when I assign 2 to the key "a" of the dictionary d, I would like to know if I can access the variable a instead of its value to modify the value of the variable a directly, accessing it through the dictionary. I.e. my expected last output would be
>>> a
2
Is there any way of doing this?
I suppose you know the idea of mutable and immutable objects. Immutable objects (str, int, float, etc) are passed by value. That's why your desired behaviour can't work. When you do:
a = 1
d["a"] = a
you just pass the value of a variable to your dict key 'a'. d['a'] knows nothing about variable a. They just both point to same primitive value in memory.
I don't know your case and why you need this behaviour, but you can try to use mutable object. For example:
class A:
def __init__(self, a: int):
self._value = a
@property
def value(self) -> int:
return self._value
@value.setter
def value(self, a: int):
# you can put some additional logic for setting new value
self._value = a
def __int__(self) -> int:
return self._value
And then you can use it in this way:
>>> a = A(1)
>>> d = {"a": a}
>>> d['a'].value
1
>>> d["a"].value = 2
>>> d['a'].value
2
>>> a.value
2
>>> int(a)
2
But it still seems like an overhead and you should rethink whether you really need this behaviour.
When you do
>>> a
, you are calling the value of the variable, a that you set on the first line. You have not changed the value of that variable, hence the output of 1. If you did
>>> d["a"]
, your output would be
>>> 2
. If you want this value to be the variable a's value too, set the value of a to the value of d["a"].
Example-
>>> a = 1
>>> d = {"a": a}
>>> d
{'a': 1}
>>> d["a"] = 2
>>> d
{'a': 2}
>>> a = d["a"]
>>> a
2
