What's the fastest way to concatenate things into a string?

Concatenating_strings.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
   "id": "e04ff53a",
   "metadata": {},
   "source": [
    "# Concatenating strings\n",
    "\n",
    "What's the fastest way to join a bunch of numbers together into a big string?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "f5ab27df",
   "metadata": {},
   "outputs": [],
   "source": [
    "def s_concat_naive(n: int) -> str:\n",
    "    \"\"\"Just loop and append, then join.\"\"\"\n",
    "    s = []\n",
    "    for i in range(n):\n",
    "        s.append(str(i))\n",
    "    return ''.join(s)\n",
    "\n",
    "n = 100_000\n",
    "s = s_concat_naive(n)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "f8ca2e3d",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "17.1 ms ± 176 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
     ]
    }
   ],
   "source": [
    "%timeit s_concat_naive(n)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "b382506c",
   "metadata": {},
   "outputs": [],
   "source": [
    "from functools import reduce\n",
    "from operator import add\n",
    "\n",
    "def s_concat_functional(n: int) -> str:\n",
    "    \"\"\"Pure functional.\"\"\"\n",
    "    return reduce(add, map(str, range(n)))\n",
    "\n",
    "assert s_concat_functional(n) == s"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "d138a454",
   "metadata": {},
   "outputs": [],
   "source": [
    "%timeit s_concat_functional(n)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "0c690f30",
   "metadata": {},
   "outputs": [],
   "source": [
    "def s_concat_preallocate(n: int) -> str:\n",
    "    \"\"\"Preallocate the list.\"\"\"\n",
    "    s = [None] * n\n",
    "    for i in range(n):\n",
    "        s[i] = str(i)\n",
    "    return ''.join(s)\n",
    "\n",
    "assert s_concat_preallocate(n) == s"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "51fabe70",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "15.7 ms ± 252 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
     ]
    }
   ],
   "source": [
    "%timeit s_concat_preallocate(n)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "fad73596",
   "metadata": {},
   "outputs": [],
   "source": [
    "def s_concat_genexpr(n: int) -> str:\n",
    "    \"\"\"Stringify in a generator expression.\"\"\"\n",
    "    return ''.join(str(i) for i in range(n))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "5004e755",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "15.1 ms ± 248 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
     ]
    }
   ],
   "source": [
    "%timeit s_concat_genexpr(n)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "668bd49f",
   "metadata": {},
   "outputs": [],
   "source": [
    "def s_concat_format(n: int) -> str:\n",
    "    \"\"\"Make the string, then pass contents via format.\"\"\"\n",
    "    meta = n * '{}'\n",
    "    return meta.format(*range(n))\n",
    "\n",
    "assert s_concat_format(n) == s"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "75ab78ba",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "6.62 ms ± 48.8 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
     ]
    }
   ],
   "source": [
    "%timeit s_concat_format(n)"
   ]
  }
 ],
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