Skip to content

Instantly share code, notes, and snippets.

@drorata

drorata/demo.ipynb

Created April 15, 2025 07:14
Show Gist options

  • Select an option

    Learn more about clone URLs
  • Save drorata/b8b6e90d846977a463761a9157be1ffb to your computer and use it in GitHub Desktop.

Select an option

Learn more about clone URLs
Save drorata/b8b6e90d846977a463761a9157be1ffb to your computer and use it in GitHub Desktop.
Download ZIP
What the HASH? Some insights into the Python built in hash function
Display the source blob
Display the rendered blob
Raw
demo.ipynb
{
"cells": [
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"hash(\"Hello hash\")"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Intro\n",
"\n",
"* Hash functions are used to (among other things) to generate identifiers of objects\n",
"* This is why it is not possible to hash a mutable object (like a list)\n",
"* The built in `hash` is designed for efficiency when using hash tables\n",
"* If `x==y` then `hash(x) == hash(y)`. Obviously, the inverse doesn't hold.\n",
"* For numbers, `hash(1) == hash(1.0)`"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Hash of integers"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"hash(1) == hash(1.0) == 1"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"hash(-290000)"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"for i in range (-5,5):\n",
" print(f\"i={i:2}\", f\"hash({i:2})={hash(i):2}\")"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Do you see something special?\n",
"\n",
"This happens [here](https://github.com/python/cpython/blob/8190571a75fc46278042e7fffbe8aeb1f71ab21d/Objects/longobject.c#L3738-L3743)"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"for N in [2**61-3, 2**61-2, 2**61-1, 2**61, 2**61+1, 2**61+2]:\n",
" print(f\"hash({N}) = {hash(N)}\")"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Hashing BaseModels"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"from pydantic import BaseModel, ConfigDict"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"class Foo(BaseModel):\n",
" bar: str\n",
" baz: int"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"hash(Foo(bar=\"string\", baz=314))"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"class Bar(BaseModel):\n",
" foo: str\n",
" baz: int\n",
"\n",
" model_config = ConfigDict(frozen=True)"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"hash(Bar(foo=\"string\", baz=123))"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"class Goo(BaseModel):\n",
" foo: str\n",
" baz: list[int]\n",
"\n",
" model_config = ConfigDict(frozen=True)"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {},
"outputs": [],
"source": [
"hash(Goo(foo=\"string\", baz=[1,2,3]))"
]
}
],
"metadata": {
"kernelspec": {
"display_name": ".venv",
"language": "python",
"name": "python3"
},
"language_info": {
"codemirror_mode": {
"name": "ipython",
"version": 3
},
"file_extension": ".py",
"mimetype": "text/x-python",
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
"version": "3.12.2"
}
},
"nbformat": 4,
"nbformat_minor": 2
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment