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#89: A tenacious episode that won't give up

Published Sat, Aug 4, 2018, recorded Thu, Aug 2, 2018

Python Bytes 89

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Brian #1: tenacity

  • “Tenacity is a general-purpose retrying library to simplify the task of adding retry behavior to just about anything.”
  • Example (Also, nice Trollhunters reference):

        import random
        from tenacity import retry
        def do_something_unreliable():
            if random.randint(0, 10) > 1:
                raise IOError("Broken sauce, everything is hosed!!!")
                return "Awesome sauce!"  # Toby says this frequently
  • Features:

    • Generic Decorator API
    • Specify stop condition (i.e. limit by number of attempts)
    • Specify wait condition (i.e. exponential backoff sleeping between attempts)
    • Customize retrying on Exceptions
    • Customize retrying on expected returned result
    • Retry on coroutines

Michael #2: Why is Python so slow?

  • Answer this question: When Python completes a comparable application 2–10x slower than another language, why is it slow and can’t we make it faster?
  • Here are the top theories:
    • “It’s the GIL (Global Interpreter Lock)”
    • “It’s because its interpreted and not compiled”
    • “It’s because its a dynamically typed language”
  • “It’s the GIL”
  • “It’s because its an interpreted language”
    • I hear this a lot and I find it a gross-simplification of the way CPython actually works.
    • JIT vs. NonJIT is interesting (startup time too)
  • “It’s because its a dynamically typed language”
    • In a “Statically-Typed” language, you have to specify the type of a variable when it is declared. Those would include C, C++, Java, C#, Go.
    • In a dynamically-typed language, there are still the concept of types, but the type of a variable is dynamic.
    • Not having to declare the type isn’t what makes Python slow
    • It’s this design that makes it incredibly hard to optimize Python.
  • Conclusion
    • Python is primarily slow because of its dynamic nature and versatility. It can be used as a tool for all sorts of problems, where more optimized and faster alternatives are probably available.

Brian #3: Keynoting with Mu

  • David Beazley gave his EuroPython talk/demo “Die Threads” using Mu.
  • Article also notes that simple tools are great not just for learning, but for teaching, as the extra clutter of a full power editor doesn’t distract too much.

Michael #4: A multi-core Python HTTP server (much) faster than Go (spoiler: Cython)

  • Exploring the question, “So, I’ve heard Python is slow… is it?”
  • A multi-core Python HTTP server that is about 40% to 110% faster than Go can be built by relying on the Cython language and LWAN C library.
  • Just a proof of concept validates the possibility of high performance system programming in the Cython language.
  • Primarily interesting as a highlight of Cython
    • Cython is both an optimizing static compiler and a hybrid language. It mainly gives the ability to:
    • write Python code that can call back and forth from and to C/C++;
    • add static typing using C declarations to Python code in order to boost performance;
    • release the GIL in some code sections.
  • Cython generates very efficient C code, which is then compiled into a module that Python can import. So it is an ideal language for wrapping external C libraries, and for developing C modules that speed up the execution of Python code.
  • However, all experiments we are aware that rely on Cython for system programming fail short in at least two ways:
    • as soon as some Python code is invoked (as opposed to pure Cython cdef code), performance degrades by one or two orders of magnitude;
    • benchmarks are most of the time provided for single core execution only, which is somehow unfair considering Golang's ability to scale up on multiple cores.

Brian #5: PyCharm 2018.2 beefs up pytest support

  • Honestly, I’m super excited about this release to help my team navigate to all of the fixtures I create on a regular basis.
  • This is the release I’ve been waiting for.
  • I can now fully utilize the power of pytest from PyCharm
  • Here’s the few things that were missing that now work great:
    • Autocomplete fixtures from various sources
    • Quick documentation and navigation to fixtures
    • Renaming a fixture from either the definition or a usage
    • Support for pytest’s parametrize
  • See also: PyCharm 2018.2 and pytest Fixtures
  • But if you really want to understand fixtures quickly, read chapters 3 and 4 of the pytest book.

Michael #6: XAR for Facebook

  • XAR lets you package many files into a single self-contained executable file. This makes it easy to distribute and install.
  • A .xar file is a read-only file system image which, when mounted, looks like a regular directory to user-space programs. This requires a one-time installation of a driver for this file system (SquashFS).
  • There are two primary use cases for XAR files.
    • Simply collecting a number of files for automatic, atomic mounting somewhere on the filesystem.
    • By making the XAR file executable and using the xarexec helper, a XAR becomes a self-contained package of executable code and its data. A popular example is Python application archives that include all Python source code files, as well as native shared libraries, configuration files, other data.
  • Advantages of XAR for Python usage
    • SquashFS looks like regular files on disk to Python. This lets it use regular imports which are better supported by CPython.
    • SquashFS looks like regular files to your application, too. You don't need to use pkg_resources or other tricks to access data files in your package.
    • SquashFS with Zstandard compression saves disk space, also compared to a ZIP file.
    • SquashFS doesn't require unpacking of .so files to a temporary location like ZIP files do.
    • SquashFS is faster to start up than unpacking a ZIP file. You only need to mount the file system once. Subsequent calls to your application will reuse the existing mount.
    • SquashFS only decompresses the pages that are used by the application, and decompressed pages are cached in the page cache.
    • SquashFS is read-only so the integrity of your application is guaranteed compared to using virtualenvs or unpacking to a temporary directory.
  • Performance is interesting too



  • numpy 1.15.0 just released recently. Switched testing to pytest.


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