Python was designed (was Re: Multi-threading in Python vs Java)

[Antoon Pardon]

Op 15-10-13 10:57, Chris Angelico schreef:
> On Tue, Oct 15, 2013 at 6:48 PM, Antoon Pardon
> <antoon.pardon at rece.vub.ac.be> wrote:
>> Op 15-10-13 01:11, Chris Angelico schreef:
>>> On Tue, Oct 15, 2013 at 6:18 AM, John Nagle <nagle at animats.com> wrote:
>>
>>>
>>>> Operator "+" as concatenation for built-in arrays but addition
>>>> for NumPy arrays.
>>>
>>> ... NumPy definitely isn't part of the language. It's not even part of
>>> the standard library, it's fully third-party.
>>
>> That doesn't matter. Adding and concating are different operations and
>> their are types in which both occur rather naturally. So as a designer
>> of such a class you have to choose for which operation you use the
>> natural python operator and for which operation you have to do it
>> differently. NumPy is just an example that you can't escape this sort
>> of incompatibilities in python.
> 
> So what should "abc" + "def" result in, if addition is different from
> concatenation?

A type error.

> No, adding strings should concatenate them. And other
> arithmetic operators make sense, too; Python doesn't happen to
> implement str-str or str/str, but some languages do:
> 
>> "abc"+"def"-"abc";
> (1) Result: "def"
>> "abc"-"b";
> (2) Result: "ac"
>> "foo bar asdf qwer"/" "*"##";
> (3) Result: "foo##bar##asdf##qwer"
> 
> PHP has separate addition and concatenation operators, and it doesn't
> help anything (granted, the biggest problem is that every other
> language we work with uses + to concat strings, so it's an easy source
> of bugs); having multiple operators for "add the elements of these
> arrays" and "add these arrays together" is really orthogonal to the
> general issue of adding and concatenating needing different operators.

No it is not, because adding elements to an array is concatenation.
If you want the array adding operator to be the same as the adding
operator for other types and you want the array concatenating operator
be the same as the concatenating operator for other types, you can
only do that if the two operations use different operators.

Since python use the same, you are forced to introduce some kind
of incompatibility.

If you have a library function that assumes '+' for concatenating
sequences and you have a library function that assumes '+' has
group like properties you can't implement your arrays in a way
they can use both.

-- 
Antoon Pardon