#194 Events and callbacks in the Python language!

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Brian #1: An introduction to mutation testing in Python

• Moshe Zadka
• This article uses mutmut, but there are other mutation testing packages.
• The example shows 3 methods, and one test case that actually hits 100% code coverage.
• The mutmut is used and finds 16 surviving mutants.
• “Mutation testing algorithmically modifies source code and checks if any "mutants" survived each test. Any mutant that survives the unit test is a problem: it means that a modification to the code, likely introducing a bug, was not caught by the standard test suite.”
• “For each mutation test, mutmut modified portions of your source code that simulates potential bugs. An example of a modification is changing a > comparison to >= to see what happens. If there is no unit test for this boundary condition, this mutation will "survive": this is a potential bug that none of the tests will detect.”
• Cool example of how to check mission critical parts of your code and the tests around them above and beyond code coverage.
• BTW, mutmut is also used codechalleng.es in the challenges asking users to write the tests.

Michael #2: asynq

• From Quora, a little old but still interesting and active
• A library for asynchronous programming in Python with a focus on batching requests to external services.
• Also provides seamless interoperability with synchronous code, support for asynchronous context managers, and tools to make writing and testing asynchronous code easier.
• Developed at Quora and is a core component of Quora's architecture.
• The most important use case for asynq is batching.
• asynq's asynchronous functions are implemented as Python generator functions. Every time an asynchronous functions yields one or more Futures, it cedes control the asynq scheduler,

Brian #3: redis: Beyond the Cache

• Guy Royse
• Some cool examples with Python code of using redis for more than a cache.
  • as a queue, with rpush and blpop
  • pub/sub, with publish and psubscribe
  • data streaming, with xadd and xread
  • as a search engine
  • and of course, as a primary in-memory database
• examples use aioredis to access with async/await

Michael #4: LittleTable

• Discovered as part of my multi-key dictionary quest (more on this later)
• By Paul McGuire
• A Python module to give ORM-like access to a collection of objects
• Provides a low-overhead, schema-less, in-memory database access to a collection of user objects.
• In addition to basic ORM-style insert/remove/query/delete access to the contents of a Table, littletable offers:
  • simple indexing for improved retrieval performance, and optional enforcing key uniqueness
  • access to objects using indexed attributes
  • simplified joins using '+' operator syntax between annotated Tables
  • the result of any query or join is a new first-class littletable Table

Brian #5: pytest-timeout

• listener suggestion
• This is essential, I think.
• Make sure no test runs longer than a certain number of seconds.
• You can set a global timeout either via command line or via a config file.
• You can specify different times for specific tests via a mark decorator
• Great stopgap to make sure no test runs forever.

Michael #6: Events

• Call me, maybe
• by Nicola Iarocci
• Adds event subscription and callback to the Python language
• Based on C# language’s events, provides a handy way to declare, subscribe to and fire events.
• Encapsulates the core to event subscription and event firing and feels like a “natural” part of the language.
• Example:

    >>> def something_changed(reason):
    ...     print(f"something changed because {reason}")

    >>> from events import Events
    >>> events = Events()
    >>> events.on_change += something_changed

• Multiple callback functions can subscribe to the same event. When the event is fired, all attached event handlers are invoked in sequence.

    >>> events.on_change('it had to happen')
    'something changed because it had to happen'

• Gist for Michael’s example:
• gist.github.com/mikeckennedy/7235543fd5964bebabe1e3546ce67d91

Extras:

Michael:

• Finished the memory management course, coming soon. Started one on Python design patterns

Brian:

• pytest 6.0.1 released
  • I walk through some of the changes in testandcode.com/125

Joke:

https://xkcd.com/327/