#176 How python implements super long integers
Published April 7, 2020
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29 min
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    Sponsored by DigitalOcean: pythonbytes.fm/digitalocean

    Topic #0: Quick chat about COVID 19

    Brian #1: What the heck is pyproject.toml?

    • Brett Cannon
    • pyproject.toml
      • PEP 517 and 518 define what this file looks like and how to use it to build projects
    • We’re familiar with it being used for flit and poetry based projects.
    • Not so much with setuptools, but it does work with setuptools.
    • You can add configuration for non-build related activities, such as coverage, tox, even though those tools support their own config files.
    • Black is gaining popularity, probably more so than the use of flit.
      • Black only uses pyproject.toml for configuration (what little config is available. But there is some.)
    • So. Project adds use of black, ends up configuring with with pyproject.toml, but not specifying build steps, No builds are broken. :(
    • Brett has the answers.
    • Add the following to pyproject.toml. Then go read the rest of Brett’s article. It’s good.
        [build-system]
        requires = ["setuptools >= 40.6.0", "wheel"]
        build-backend = "setuptools.build_meta"
    

    Michael #2: Awesome Python Bytes Awesome List

    • By Jack McKew
    • Will be adding to this repo whenever I hear about awesome packages (in my opinion), PRs are welcome for anyone else though!
    • Already has 5 PRs accepted
    • Comes with graphics!!! Like all good presentations should.
    • Some fun projects this made me recall:
      • Great Expectations - for validating, documenting, and profiling, your data
      • pandas-vet - a plugin for flake8 that provides opinionated linting for pandas code.
      • GeoAlchemy - Using SQLAlchemy with Spatial Databases.
      • vue.py - Provides Python bindings for Vue.js. It uses brython to run Python in the browser.
    • Remember we have speedy search for our content over at pythonbytes.fm/search

    Brian #3: Publishing package distribution releases using GitHub Actions CI/CD workflows

    • PyPA
    • You’ve moved to flit (or not) and started using GitHub actions to build and test whenever you push to GitHub. So awesome.
    • But now, there’s still a manual step to remember to publish to PyPI.
    • And maybe we should be checking publish more often with the Test PyPI server.
    • This article is a step by step walkthrough.
    • It’s a bit dated, 3.7. So I’m trying to walk through all the steps with my cards project and it will be finished by the time this episode goes live.
    • Stumbling blocks right now:
      • I’ve left my email blank, no email for author or maintainer in pyproject.toml, because neither flit, nor pip require it. But PyPI still does. grrrr.
        • Trying to decide between: normal email, setting up a new email for it, using a me+pypi gmail alias, setting up a new email address just for pypi, etc.
      • test pypi fails due to “file already exists”, so, that’s always gonna be the case unless I bump the version, so gonna have to try to figure out a way around that.

    Michael #4: Rich text for terminals

    • Rich is a Python library for rich text and beautiful formatting in the terminal.
    • Add colorful text (up to 16.7 million colors) with styles (bold, italic, underline etc.) to your script or application.
    • Rich can also render pretty tables, progress bars, markdown, syntax highlighted source code, and tracebacks -- out of the box.
    • Centered or justified text
    • Tables, tables!
    • Syntax highlighted code
    • Markdown!
    • Can replace print() and does pretty printing of dictionaries with color.
    • Good Windows support for the new Windows Terminal

    Brian #5: psutil: Cross-platform lib for process and system monitoring in Python

    • “psutil (process and system utilities) is a cross-platform library for retrieving information on running processes and system utilization (CPU, memory, disks, network, sensors) in Python. It is useful mainly for system monitoring, profiling and limiting process resources and management of running processes. It implements many functionalities offered by classic UNIX command line tools such as ps, top, iotop, lsof, netstat, ifconfig, free and others.”
    • Useful for an incredible amount of information about the system you are running on:
      • cpu times, stats, load, number of cores
      • memory size and usage
      • disk partitions, usage
      • sensors, including battery
      • users
      • processes and process management
        • getting ids, names, etc.
        • cpu, memory, connections, files, threads, etc per process
        • signaling processes, like suspend, resume, kill

    Michael #6: How python implements super long integers

    • by Arpit Bhayani
    • In C, you worry about picking the right data type and qualifiers for your integers; at every step, you need to think if int would suffice or should you go for a long or even higher to a long double.
    • In python, you need not worry about these "trivial" things because python supports integers of arbitrary size.
    • 2 ** 20000 in C is INF where as in Python’s it’s fine, just at 6,021 digit result. But how!?!
    • Integers are represented as:
        typedef struct {
            PyObject ob_base;
            Py_ssize_t ob_size; /* Number of items in variable part */
        } PyVarObject;
    
    • Other types that has PyObject_VAR_HEAD are
      • PyBytesObject
      • PyTupleObject
      • PyListObject
        # Python's number:
        struct _longobject {
            PyObject ob_base;
            Py_ssize_t ob_size; /* Number of items in variable part */
            digit ob_digit[1];
        };
    
    • A "digit" is base 230 hence if you convert 1152921504606846976 into base 230 you get 100
    • Operations on super long integers
      • Addition: Integers are persisted "digit-wise", this means the addition is as simple as what we learned in the grade school
      • Subtraction: Same
      • Multiplication: In order to keep things efficient implements the Karatsuba algorithm that multiplies two n-digit numbers in O(nlog23) elementary steps.
    • Optimization of commonly-used integers: Python preallocates small integers in a range of -5 to 256. This allocation happens during initialization

    Extras:

    Michael:

    • We're coming to YouTube, probably. :)
    • npm is joining GitHub

    Joke:

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