On 2005-11-30, Duncan Booth <[EMAIL PROTECTED]> wrote:
> Antoon Pardon wrote:
>> But lets just consider. Your above code could simply be rewritten
>> as follows.
>>
>> res = list()
>> for i in range(10):
>> res.append(i*i)
>>
> I don't understand your point here? You want list() to create a new list
> and [] to return the same (initially empty) list throughout the run of the
> program?
No, but I think that each occurence returning the same (initially empty)
list throughout the run of the program would be consistent with how
default arguments are treated.
>
>> Personnaly I think that the two following pieces of code should
>> give the same result.
>>
>> def Foo(l=[]): def Foo(l):
>> ... ...
>>
>> Foo() Foo([])
>> Foo() Foo([])
>>
>> Just as I think, you want your piece of code to give the same
>> result as how I rewrote it.
>>
>> I have a problem understanding people who find the below don't
>> have to be equivallent and the upper must.
>
> The left one is equivalent to:
>
> __anon = []
> def Foo(l):
> ...
>
> Foo(__anon)
> Foo(__anon)
So, why shouldn't:
res = []
for i in range(10):
res.append(i*i)
be equivallent to:
__anon = list()
...
res = __anon
for i in range(10):
res.append(i*i)
> The left has one list created outside the body of the function, the right
> one has two lists created outside the body of the function. Why on earth
> should these be the same?
Why on earth should it be the same list, when a function is called
and is provided with a list as a default argument?
I see no reason why your and my question should be answered differently.
> Or to put it even more simply, it seems that you are suggesting:
>
> __tmp = []
> x = __tmp
> y = __tmp
>
> should do the same as:
>
> x = []
> y = []
No, I'm not suggesting it should, I just don't see why it should be
considered a problem if it would do the same, provided this is the
kind of behaviour we already have with list as default arguments.
Why is it a problem when a constant list is mutated in an expression,
but isn't it a problem when a constant list is mutated as a default
argument?
--
Antoon Pardon
--
http://mail.python.org/mailman/listinfo/python-list
