Augument assignment versus regular assignment

[Kirk McDonald]

Frank Millman wrote:
> nagy wrote:
> 
>>Thanks, Kirk.
>>I considered the += as only a shorthand notation for the assignment
>>operator.
>>Since for lists + is simply a concatetation, I am not sure it x=x+[2]
>>is creating a brand
>>new list. Could you refer me to any documentation on this?
>>Thanks,
>>Nagy
> 
> 
> My habit is to check the id.
> 
> 
>>>>x = [1,2]
>>>>id(x)
> 
> -1209327188
> 
>>>>x += [4]
>>>>x
> 
> [1,2,4]
> 
>>>>id(x)
> 
> -1209327188
> 
>>>>x = x + [6]
>>>>x
> 
> [1,2,4,6]
> 
>>>>id(x)
> 
> -1209334664
> 
> So it looks as if x +=  [] modifies the list in place, while x = x + []
> creates a new list.
> 
> I am not sure if this is 100% guaranteed,

It is. This is true for any mutable type.

> as I have noticed in the past
> that id's can be reused under certain circumstances. Perhaps one of the
> resident gurus can comment.
>