Example around mutable default values of functions

demo.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "from typing import Any"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Wrong 💥"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add_value(new_val: Any, my_list: list[Any] = []):\n",
    "    print(f\"{my_list = }\")\n",
    "    print(f\"{id(my_list) = }\")\n",
    "    my_list.append(new_val)\n",
    "    return my_list"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(new_val=\"bar\", my_list=[\"foo\",])\n",
    "f\"{res = }\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(new_val=\"foo\")\n",
    "res"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(new_val=\"foo\")\n",
    "res"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Right! 🚀"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add_value(new_val, my_list: list[Any] | None = None):\n",
    "    if my_list is None:\n",
    "        my_list = []\n",
    "\n",
    "    print(f\"{my_list = }\")\n",
    "    print(f\"{id(my_list) = }\")\n",
    "    my_list.append(new_val)\n",
    "    print(my_list)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(new_val=\"foo\")\n",
    "res"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(new_val=\"foo\")\n",
    "res"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# What about immutable❓"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add_value(new_val, my_tuple: tuple[Any] = tuple()):\n",
    "    print(f\"{my_tuple = }\")\n",
    "    print(f\"{id(my_tuple) = }\")\n",
    "    # my_tuple.append(new_val)\n",
    "    my_tuple += (new_val, )\n",
    "    print(f\"{id(my_tuple) = }\")\n",
    "    return my_tuple"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(new_val=\"foo\")\n",
    "res"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(new_val=\"foo\")\n",
    "res"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "res = add_value(\"bar\", my_tuple=(\"foo\",))\n",
    "res"
   ]
  }
 ],
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