Python/Django 模型字典允许一种类型的更新，但不允许另一种类型的更新

Question

I am working on some Django/Python code.

Basically, the backend of my code gets sent a dict of parameters named 'p'. These values all come off Django models.

When I tried to override them as such:

p['age']=25

I got a 'model error'. Yet, if I write:

p.age=25

it works fine.

My suspicion is that, internally, choice #1 tries to set a new value to an instance of a class created by Django that objects to being overridden, but internally Python3 simply replaces the Django instance with a "new" attribute of the same name ('age'), without regard for the prior origin, type, or class of what Django created.

All of this is in a RESTful framework, and actually in test code. So even if I am right I don't believe it changes anything for me in reality.

But can anyone explain why one type of assignment to an existing dict works, and the other fails?

Answer 1

p is a class, not a dict. Django built it that way.

But, as such, one approach (p.age) lets you change an attribute of the object in the class.