Re: Python (was Re: Recent history of vi)

candycanearter07 <[email protected]>
writes:
> Lawrence D’Oliveiro <[email protected]> wrote at 02:05 this Sunday (GMT):
>> On 13 Dec 2025 11:55:35 GMT, Stéphane CARPENTIER wrote:
>>> Everything else is just a lot of lies. They pretend it's not
>>> strongly typed, but in the real world you will only encounter a lot
>>> of issue if you believe that.
>>
>> Think about why both JavaScript and PHP need a “===” operator, while
>> Python does not.
>>
>> It’s because Python is strongly typed.
>
> I thought it was because JS was too liberal with type-casting to make
> things true, and the JS devs didn't want to break compatibility.

“No implicit type conversion” is one of the definitions of strong
typing, at least back to the 1970s[1]. And JavaScript is certainly
weakly typed in that sense:

    > 'a' + 1
    'a1'
    > 1/false
    Infinity

What dividing by a boolean could possibly mean is a mystery, but
JavaScript will do it anyway.

Python fits this definition of strong typing up to a point:

    >>> 'a' + 1
    Traceback (most recent call last):
      File "<python-input-0>", line 1, in <module>
        'a' + 1
        ~~~~^~~
    TypeError: can only concatenate str (not "int") to str

However it only goes so far, for example many things will implicitly
convert to bool:

    >>> not ''
    True
    >>> not {}
    True

When you define your own classes, you can arrange for them to perform
arithmetic with other types without explicit conversions too.

Another property suggested in [1] for ‘strong typing’ is that functions
can only be called with with arguments matching a declared type. In
Python, function arguments do not have declared types[2] and does not
even infer them; anything goes. You will only hit an exception if you
try to use the arguments in the wrong way.

    >>> def f(a,b):
    ...     return a + b
    ...
    >>> f("a", "a")
    'aa'
    >>> f(0,0)
    0
    >>> f("a", 0)
    Traceback (most recent call last):
      File "<python-input-4>", line 1, in <module>
        f("a", 0)
        ~^^^^^^^^
      File "<python-input-0>", line 2, in f
        return a + b
               ~~^~~
    TypeError: can only concatenate str (not "int") to str

[1] https://dl.acm.org/doi/epdf/10.1145/942572.807045

[2] you can put in type annotations but the language implementation
    ignores them - you need to run a separate static checker.

I would say that although Python does have some aspects of strong
typing, it is mostly weakly typed.

-- 
https://www.greenend.org.uk/rjk/