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From: Marko Rauhamaa <marko@pacujo.net>
Newsgroups: comp.lang.python
Subject: Re: What is a function parameter =[] for?
Date: Thu, 19 Nov 2015 20:39:38 +0200
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BartC <bc@freeuk.com>:

> Yes. In the languages I create, pretty much everything is mutable,
> provided it can supply an l-value. Constructs such as those for empty
> lists ([] in Python, () in mine) aren't l-values.
>
> But it doesn't apply default values.

Python's default-value semantics is analogous to C++:

========================================================================
#include <iostream>

using namespace std;

static int z;

static void f(int &x = z)
{
    x++;
}

int main()
{
    cout << z << endl;
    f();
    cout << z << endl;
    f();
    cout << z << endl;
    return 0;
}
========================================================================

which prints:

    0
    1
    2


Marko