mypy VS CPython

Compare mypy vs CPython and see what are their differences.

Our great sponsors
  • InfluxDB - Power Real-Time Data Analytics at Scale
  • WorkOS - The modern identity platform for B2B SaaS
  • SaaSHub - Software Alternatives and Reviews
mypy CPython
112 1302
17,410 59,047
1.8% 1.7%
9.8 10.0
about 4 hours ago 3 days ago
Python Python
GNU General Public License v3.0 or later GNU General Public License v3.0 or later
The number of mentions indicates the total number of mentions that we've tracked plus the number of user suggested alternatives.
Stars - the number of stars that a project has on GitHub. Growth - month over month growth in stars.
Activity is a relative number indicating how actively a project is being developed. Recent commits have higher weight than older ones.
For example, an activity of 9.0 indicates that a project is amongst the top 10% of the most actively developed projects that we are tracking.

mypy

Posts with mentions or reviews of mypy. We have used some of these posts to build our list of alternatives and similar projects. The last one was on 2024-03-11.
  • The GIL can now be disabled in Python's main branch
    8 projects | news.ycombinator.com | 11 Mar 2024
  • Polars – A bird's eye view of Polars
    4 projects | news.ycombinator.com | 13 Feb 2024
    It's got type annotations and mypy has a discussion about it here as well: https://github.com/python/mypy/issues/1282
  • Python 3.13 Gets a JIT
    11 projects | news.ycombinator.com | 9 Jan 2024
    There is already an AOT compiler for Python: Nuitka[0]. But I don't think it's much faster.

    And then there is mypyc[1] which uses mypy's static type annotations but is only slightly faster.

    And various other compilers like Numba and Cython that work with specialized dialects of Python to achieve better results, but then it's not quite Python anymore.

    [0] https://nuitka.net/

    [1] https://github.com/python/mypy/tree/master/mypyc

  • Introducing Flask-Muck: How To Build a Comprehensive Flask REST API in 5 Minutes
    3 projects | dev.to | 20 Dec 2023
  • It's Time for a Change: Datetime.utcnow() Is Now Deprecated
    5 projects | news.ycombinator.com | 19 Nov 2023
    It's funny you should say this.

    Reading this article prompted me to future-proof a program I maintain for fun that deals with time; it had one use of utcnow, which I fixed.

    And then I tripped over a runtime type problem in an unrelated area of the code, despite the code being green under "mypy --strict". (and "100% coverage" from tests, except this particular exception only occured in a "# pragma: no-cover" codepath so it wasn't actually covered)

    It turns out that because of some core decisions about how datetime objects work, `datetime.date.today() < datetime.datetime.now()` type-checks but gives a TypeError at runtime. Oops. (cause discussed at length in https://github.com/python/mypy/issues/9015 but without action for 3 years)

    One solution is apparently to use `datetype` for type annotations (while continuing to use `datetime` objects at runtime): https://github.com/glyph/DateType

  • What's New in Python 3.12
    5 projects | news.ycombinator.com | 18 Oct 2023
    PEP 695 is great. I've been using mypy every day at work in last couple years or so with very strict parameters (no any type etc) and I have experience writing real life programs with Rust, Agda, and some Haskell before, so I'm familiar with strict type systems. I'm sure many will disagree with me but these are my very honest opinions as a professional who uses Python types every day:

    * Some types are better than no types. I love Python types, and I consider them required. Even if they're not type-checked they're better than no types. If they're type-checked it's even better. If things are typed properly (no any etc) and type-checked that's even better. And so on...

    * Having said this, Python's type system as checked by mypy feels like a toy type system. It's very easy to fool it, and you need to be careful so that type-checking actually fails badly formed programs.

    * The biggest issue I face are exceptions. Community discussed this many times [1] [2] and the overall consensus is to not check exceptions. I personally disagree as if you have a Python program that's meticulously typed and type-checked exceptions still cause bad states and since Python code uses exceptions liberally, it's pretty easy to accidentally go to a bad state. E.g. in the linked github issue JukkaL (developer) claims checking things like "KeyError" will create too many false positives, I strongly disagree. If a function can realistically raise a "KeyError" the program should be properly written to accept this at some level otherwise something that returns type T but 0.01% of the time raises "KeyError" should actually be typed "Raises[T, KeyError]".

    * PEP 695 will help because typing things particularly is very helpful. Often you want to pass bunch of Ts around but since this is impractical some devs resort to passing "dict[str, Any]"s around and thus things type-check but you still get "KeyError" left and right. It's better to have "SomeStructure[T]" types with "T" as your custom data type (whether dataclass, or pydantic, or traditional class) so that type system has more opportunities to reject bad programs.

    * Overall, I'm personally very optimistic about the future of types in Python!

    [1] https://github.com/python/mypy/issues/1773

  • Mypy 1.6 Released
    5 projects | news.ycombinator.com | 17 Oct 2023
  • Ask HN: Why are all of the best back end web frameworks dynamically typed?
    4 projects | news.ycombinator.com | 5 Oct 2023
    You probably already know but you can add type hints and then check for consistency with https://github.com/python/mypy in python.

    Modern Python with things like https://learnpython.com/blog/python-match-case-statement/ + mypy + Ruff for linting https://github.com/astral-sh/ruff can get pretty good results.

    I found typed dataclasses (https://docs.python.org/3/library/dataclasses.html) in python using mypy to give me really high confidence when building data representations.

  • Sharing Saturday #472
    7 projects | /r/roguelikedev | 23 Jun 2023
    The in-progress tutorial is here in the official documentation. It sucks that I can never seem to make quick progress on this. Trying to do something clever with Protocols ended up with me making a pull request on the Mypy project for something that likely wasn't critical after all.
  • Writing Python like it's Rust
    10 projects | news.ycombinator.com | 21 May 2023
    I'm also 100% convinced most people who use mypy don't realize the myriad ways it just silently stopps typing things or just silently crashes with a 0 exit code. Even if you configure it to warn untyped functions etc. It will still just not work properly in some of circumstances and you will literally never know until you debug a bug that just happened to trigger it. There are over 1.4k open but tickets it's such a broken piece of software: https://github.com/python/mypy/issues?q=is%3Aissue+is%3Aopen...

    The involvement of Guido in mypy is such a tragedy.

CPython

Posts with mentions or reviews of CPython. We have used some of these posts to build our list of alternatives and similar projects. The last one was on 2024-03-15.
  • Open source at Fastly is getting opener
    10 projects | dev.to | 15 Mar 2024
    Through the Fast Forward program, we give free services and support to open source projects and the nonprofits that support them. We support many of the world’s top programming languages (like Python, Rust, Ruby, and the wonderful Scratch), foundational technologies (cURL, the Linux kernel, Kubernetes, OpenStreetMap), and projects that make the internet better and more fun for everyone (Inkscape, Mastodon, Electronic Frontier Foundation, Terms of Service; Didn’t Read).
  • C++ Safety, in Context
    8 projects | news.ycombinator.com | 12 Mar 2024
    In my understanding, no. I believe it was bpo-4489 [1], and I couldn't find a matching advisory from the PSF's database [2] which should contain all historical advisories as well.

    [1] https://github.com/python/cpython/issues/48739

    [2] https://github.com/psf/advisory-database/

  • The GIL can now be disabled in Python's main branch
    8 projects | news.ycombinator.com | 11 Mar 2024
  • Eloquent JavaScript 4th edition (2024)
    10 projects | news.ycombinator.com | 7 Mar 2024
    How do you mean? CPython uses karatsuba's for large numbers which should be asymptotically fast

    https://github.com/python/cpython/blob/d864b0094f9875c5613cb...

  • Top Paying Programming Technologies 2024
    19 projects | dev.to | 6 Mar 2024
    24. Python - $78,331
  • What is really an API? Examples, Code + History
    3 projects | dev.to | 3 Mar 2024
    a. Setting Up: Make sure you have Python and pip (package installer) installed. If you do not have Python, you can install the latest version from the Python ecosystem here
  • How to make a turtle racing game in Python
    2 projects | dev.to | 29 Feb 2024
    First, if you don't have Python installed on your machine, go to python.org to download the latest version of Python and then install it right away.
  • PySimpleGUI 4 will be sunsetted in Q2 2024
    7 projects | news.ycombinator.com | 14 Feb 2024
    You missed that they gave an example that does work—Java Swing is bundled with the JVM, making it more or less part of the standard library. Python itself also has Tkinter, which exists inside the cpython repo and is installed with Python [0].

    C++ may not work, but most other languages (especially VM-based) can and many do.

    [0] https://github.com/python/cpython/blob/3.12/Lib/tkinter/__in...

  • Memray – A Memory Profiler for Python
    10 projects | news.ycombinator.com | 10 Feb 2024
    I collected a list of profilers (also memory profilers, also specifically for Python) here: https://github.com/albertz/wiki/blob/master/profiling.md

    Currently I actually need a Python memory profiler, because I want to figure out whether there is some memory leak in my application (PyTorch based training script), and where exactly (in this case, it's not a problem of GPU memory, but CPU memory).

    I tried Scalene (https://github.com/plasma-umass/scalene), which seems to be powerful, but somehow the output it gives me is not useful at all? It doesn't really give me a flamegraph, or a list of the top lines with memory allocations, but instead it gives me a listing of all source code lines, and prints some (very sparse) information on each line. So I need to search through that listing now by hand to find the spots? Maybe I just don't know how to use it properly.

    I tried Memray, but first ran into an issue (https://github.com/bloomberg/memray/issues/212), but after using some workaround, it worked now. I get a flamegraph out, but it doesn't really seem accurate? After a while, there don't seem to be any new memory allocations at all anymore, and I don't quite trust that this is correct.

    There is also Austin (https://github.com/P403n1x87/austin), which I also wanted to try (have not yet).

    Somehow this experience so far was very disappointing.

    (Side node, I debugged some very strange memory allocation behavior of Python before, where all local variables were kept around after an exception, even though I made sure there is no reference anymore to the exception object, to the traceback, etc, and I even called frame.clear() for all frames to really clear it. It turns out, frame.f_locals will create another copy of all the local variables, and the exception object and all the locals in the other frame still stay alive until you access frame.f_locals again. At that point, it will sync the f_locals again with the real (fast) locals, and then it can finally free everything. It was quite annoying to find the source of this problem and to find workarounds for it. https://github.com/python/cpython/issues/113939)

  • Setting Up the Environment
    2 projects | dev.to | 15 Jan 2024
    Python, a versatile and powerful programming language, can be easily installed from its official website: https://www.python.org/. This section will guide you through the installation process on various operating systems, including Windows, macOS, and Linux.

What are some alternatives?

When comparing mypy and CPython you can also consider the following projects:

pyright - Static Type Checker for Python

ruff - An extremely fast Python linter and code formatter, written in Rust.

RustPython - A Python Interpreter written in Rust

pyre-check - Performant type-checking for python.

black - The uncompromising Python code formatter

pytype - A static type analyzer for Python code

pydantic - Data validation using Python type hints

Flake8 - flake8 is a python tool that glues together pycodestyle, pyflakes, mccabe, and third-party plugins to check the style and quality of some python code.

typing - Python static typing home. Hosts the documentation and a user help forum.

ipython - Official repository for IPython itself. Other repos in the IPython organization contain things like the website, documentation builds, etc.

Vulpix - Fast, unopinionated, minimalist web framework for .NET core inspired by express.js

PythonBuddy - 1st Online Python Editor With Live Syntax Checking and Execution