[Tutor] Fwd: Re: would someone please explain this concept to me

[nathan tech]

Hi alan,

thanks so much for clearing that up.

Now you've explained it in that way, I understand what it is doing and 
how it went wrong.

Thank you so much!

Nathan

On 06/06/2019 00:57, Alan Gauld via Tutor wrote:
> On 05/06/2019 20:47, nathan tech wrote:
>
>> so for example if I do:
>>
>> feeds[feed1]["limit"]=g.checklimit
>>
>> And later did g.checklimit=7000
>>
>> Would it change feeds[feed1]["limit"] too?
> No, because the feeds value is still referencing the
> original value object. The issue arises when you modify a mutable
> object that is references by two (or more) variables. If the value
> is immutable then the references will retain the original value.
>
> Specifically, in your case.
> The first example you set the feeds value to a dictionary. Then you
> modified the contents of the dictionary but did not change the
> dictionary itself.
>
> base_dict = {}   # create object
> feeds['foo'] = base_dict   # reference to same dict object
> base_dict['x'] = bar       # modified dict referred to by both variables
>
>
> But in the second example you actially change the object
> that checklimit refers to.
>
> checklimit = 22   # immutable value assigned
> feeds['bar'] = checklimit   # both refer to same immutable value
> base_var = 66   # now feeds refers to original object: 22
>                  # and checklimit refers to new object: 66
>
> In the first case you do not change the object that base_dict refers to,
> you only change its content. In the second case you make checklimit
> refer to a completely new object.
>
> Does that make sense?
>
> PS. Notice that the use of a globals module, g, is completely irrelevant
> to this issue. It has nothing to do with the values being in a module,
> the issue is purely about references to objects and whether you modify
> the referenced object or its contents.
>