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Episode #73: This podcast comes in any color you want, as long as it's black

Published Thurs, Apr 12, 2018, recorded Wed, Apr 4, 2018.

Sponsored by Datadog:

Brian #1: Set Theory and Python

  • “Let’s talk about sets, baby …” is what I have in my head while reading this.
  • Great overview of set theory and how to use the set data type in Python.
  • Covered:
    • Creating sets
    • Checking for containment (in, not in)
    • union : set of things in either set or in both
    • intersection: set of things in 2 sets
    • difference: set of things in one set but not the other
    • symmetric difference: set of things in either set but not in both

Michael #2: Trio: async programming for humans and snake people

  • The Trio project’s goal is to produce a production-quality, permissively licensed, async/await-native I/O library for Python. Like all async libraries, its main purpose is to help you write programs that do multiple things at the same time with parallelized I/O.
  • Compared to other libraries, Trio attempts to distinguish itself with an obsessive focus on usability and correctness.
  • Concurrency is complicated; we try to make it easy to get things right.
  • Trio was built from the ground up to take advantage of the latest Python features
  • Inspiration from many sources, in particular Dave Beazley’s Curio
  • Resulting design is radically simpler than older competitors like asyncio and Twisted, yet just as capable.
  • We do encourage you do use it, but you should read and subscribe to issue #1 to get warning and a chance to give feedback about any compatibility-breaking changes.
  • Excellent scalability: trio can run 10,000+ tasks simultaneously without breaking a sweat, so long as their total CPU demands don’t exceed what a single core can provide.
  • Supports Python 3.5+ and PyPy
  • Uses, 3)
    trio.sleep(1.5) # Sleep, non-blocking

    async with trio.open_nursery() as nursery:
        print("parent: spawning child...")
        print("parent: spawning child...")
        print("parent: waiting for children to finish...")
        # -- we exit the nursery block here --
    print("parent: child_func1 and child_func2 done!")

Brian #3: black: The uncompromising Python code formatter

  • An amusing take on code formatting. From the readme:

    • Black is the uncompromising Python code formatter. By using it, you agree to cease control over minutiae of hand-formatting. In return, Black gives you speed, determinism, and freedom from pycodestyle nagging about formatting. You will save time and mental energy for more important matters.”
    • “Blackened code looks the same regardless of the project you're reading. Formatting becomes transparent after a while and you can focus on the content instead.”
    • Black makes code review faster by producing the smallest diffs possible.”
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Michael #4: gain: Web crawling framework based on asyncio

  • Web crawling framework for everyone. Written with asyncio, uvloop and aiohttp.
  • Simple and mostly automated
    • Define class mapped to CSS selectors and data to save
    • Concurrently level
    • Start URL
    • Page templates to match URLs
    • Run

Brian #5: Generic Function in Python with Singledispatch

  • “Imagine, you can write different implementations of a function of the same name in the same scope, depending on the types of arguments. Wouldn’t it be great? Of course, it would be. There is a term for this. It is called “Generic Function”. Python recently added support for generic function in Python 3.4 (PEP 443). They did this to the functools module by adding @singledispatch decorator.”
  • For people less familiar with “generic functions”. I think of this as providing similar functionality as C++’s function overloading.
  • Allows you do things like this (full code example is in the article):
    from functools import singledispatch

    def fprint(data):
        "code for default functionality"

    def _(data):
        "code for list, set, tuple"

    def _(data):
        "code for dict"

More complete code example:

    from functools import singledispatch

    def fprint(data):
        print(f'({type(data).__name__}) {data}')

    def _(data):
        formatted_header = f'{type(data).__name__} -> index : value'
        print('-' * len(formatted_header))
        for index, value in enumerate(data):
            print(f'{index} : ({type(value).__name__}) {value}')

    def _(data):
        formatted_header = f'{type(data).__name__} -> key : value'
        print('-' * len(formatted_header))
        for key, value in data.items():
            print(f'({type(key).__name__}) {key}: ({type(value).__name__}) {value}')

    # >>> fprint('hello')
    # (str) hello

    # >>> fprint(21)
    # (int) 21


    # >>> fprint({'name': 'John Doe', 'age': 32, 'location': 'New York'})
    # dict -> key : value
    # -------------------
    # (str) name: (str) John Doe
    # (str) age: (int) 32
    # (str) location: (str) New York

Michael #6: Unsync: Unsynchronizing async/await in Python 3.6

  • A rant about async/await in Python (by Alex Sherman)
  • What’s wrong?
    • The two big friction points I’ve had are:
      • Difficult to “fire and forget” async calls (need to specifically run the event loop)
      • Can’t do blocking calls to asyncio.Future.result() (it throws an exception)
    • We need to acquire an even loop, do some weird call to execute the async function in that event loop, and then synchronously execute the event loop ourselves.
  • What can we do?
    • C# had this great idea of executing each Task (their version of a Future) first synchronously in the main thread until an await is hit, and then queueing it into an ambient thread pool to continue later possibly in a separate thread.
    • Python did not take this approach and my hunch is that the Python maintainers didn’t want to add an ambient thread pool to their language (which makes sense).
    • Alex, however, is not the Python maintainers and did add an ambient thread (singular). I stuffed all the boiler plate into a decorator and the result looks like this:
    async def unsync_async():
        await asyncio.sleep(0.1)
        return 'I like decorators'

  • using @unsync on a regular function (not an async one) will cause it to be executed in a ThreadPoolExecutor.
  • To support CPU bound workloads, you can use @unsync(cpu_bound=True) to decorate functions which will be executed in a ProcessPoolExecutor

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