Kostja P kpavlovsky

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

These links no longer work. Springer have pulled the free plug.

Graduate texts in mathematics

duplicates = multiple editions

A Classical Introduction to Modern Number Theory, Kenneth Ireland Michael Rosen

How to debug Python programs?

When we can’t understand the execution path or behaviour of our program we better use a debugger. Python offers pdb, a full featured debugger. Here is how to get started.

Import it with:

import pdb

How to batch rename files with bash?

Let’s say we have these files:

ls 
to_be_renamed_1.txt 
to_be_renamed_2.txt 
to_be_renamed_3.txt

	from __future__ import with_statement # we'll use this later, has to be here
	from argparse import ArgumentParser

	import requests
	from BeautifulSoup import BeautifulStoneSoup as Soup

	def parse_sitemap(url):
	resp = requests.get(url)

	# we didn't get a valid response, bail

	import hashlib, base64, hmac


	def get_proxy_signature(query_dict, secret):
	"""
	Calculate the signature of the given query dict as per Shopify's documentation for proxy requests.
	See: http://docs.shopify.com/api/tutorials/application-proxies#security
	"""

	# Sort and combine query parameters into a single string.

	class ExampleFormMultipleView(MultipleFormsView):
	template_name = 'preferences/change_group_multiple.html'
	forms = {
	'profile': ProfileForm,
	'avatar': AvatarForm,
	'contacts': ContactsForm,
	}

	def forms_valid(self, forms):
	for key, form in forms.items():

	#!/usr/bin/env bash

	# Colours picked from https://robinpowered.com/blog/best-practice-system-for-organizing-and-tagging-github-issues/

	###
	# Label definitions
	###
	declare -A LABELS

	# Platform

	Top section is for regular Ubuntu installs. Bottom section is for EC2 installs.

	Ubuntu Login as Root (regular Ubuntu VM or PC – not using AWS EC2)

	Login with main user

	Now gain root access to bash, by emulating it with sudo

	# sudo -i

	print("UPDATE AUG 2023: this script is beyond old and broken")
	print("You may find interesting and more up to date resources in the comments of the gist")
	exit()

	from slacker import Slacker
	import json
	import argparse
	import os

	# This script finds all channels, private channels and direct messages