28 Feb 2020

Determining if you are a low performer

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How can you tell if you are a low performer?

I always prefer to compare myself against my prior self and not against others. Thus, I would consider myself a low performer if my throughput is lower than what it has been on average in the past. This may happen for many reasons, amongst them it would be because I'm learning something new, so I'm spending a good chunk of my time on learning and less on executing. It might be because I'm trying different ideas to find the best one because I'm working on something I've never worked before.

It's generally easy for a programmer to tell whether he's been more or less productive than the prior week. It is mostly based on feelings, where you feel good when you are productive and less good when you're not making any progress or facing issues.

If you think and feel that you are performing poorly, start recording more thoroughly what you are working on. Identify when you start and finish working on a task, and when you get blocked, write down why. After a few weeks, look at what you wrote and assess what might cause you to feel that you are a low performer. Is it because you're working on a task you are not good at? Is it because of a lack of motivation on the task you've been assigned to?

With more information in hand to determine why you feel that you are a low performer, you will be able to devise a plan so that you can once again feel like a high performer.

28 Feb 2020

Pytest with tests files with similar names

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I have two test files with the same name and pytest complains. How do I make it work without changing the test filenames?

Example directory structure

/path/to/project/tests
├── a/
│   └── test_a.py
└── b/
    └── test_a.py

Error message:

import file mismatch:
imported module 'test_a' has this __file__ attribute:
  /path/to/project/tests/a/test_a.py
which is not the same as the test file we want to collect:
  /path/to/project/tests/b/test_a.py
HINT: remove __pycache__ / .pyc files and/or use a unique basename for your test file modules

Add a __init__.py to each directories with tests files that have the same name. Technically, you only to have a __init__.py file in one of the two directories, so that one is in a package while the other one is in a different one. Adding it in both simply prevents this issue from occurring again if you were to add a third file test_a.py.

/path/to/project/tests
├── a/
│   ├── __init__.py
│   └── test_a.py
└── b/
    ├── __init__.py
    └── test_a.py
27 Feb 2020

Identifying python files with no coverage

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I use pytest with coverage and I want to see the files that have no coverage.

It appears that pytest and pytest-cov will not list someof the files that are under namespace packages, while it will work fine for files in regular packages (see PEP 420 on the topic of implicit namespace packages).

To fix this problem, one solution is to add __init__.py files in all of your directories in order to create regular packages.

If you are using PyCharm Professional, you can simply run your test with coverage. This will allow you to identify all the files that have currently no coverage as they will appear with coverage = 0%.

27 Feb 2020

User demo walkthrough

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What should be defined to make a user demo walkthrough successful?

You need to define what you want to learn from the demo walkthrough: where does the user ask questions? where does he stay stuck? what is easy/hard for him to do? what does he think about when he goes through the demo? what is/isn't working? what frustrates him? where does the user want to have more guidance?

The user doing the walkthrough should be as close as possible to the ideal user otherwise you may get feedback that is biased on their own experience. A user with too much knowledge compared to your target user will be able to do many things your target user may need help with and they may assume a lot of things because they know about them. On the other hand, a user with too little knowledge will require help in many places where the target user is expected to have knowledge, which may make the demo walkthrough slower than desired.

The walkthrough should have a clear scenario. You may only give an initial setup to the user and a desired goal and let them figure everything out by themselves. You may also go with a more directed approach, where you tell them what to do and you see if the instructions are clear enough to accomplish the steps. The first approach is interesting because it allows you to observe variability in how to solve a problem.

26 Feb 2020

Accelerate slow pytests

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My pytests take a while to complete, how can I speed up the process?

A fairly cheap solution is to use parallelization to run your tests on multiple CPUs instead of the 1 cpu used by default. To do so, you can install pytest-xdist. Once the extension is specified, all you need to do is add -n auto when you call pytest.

Another thing you should do that requires more effort is to investigate which of your tests are consuming a lot of CPU time to execute. To do so, use the --durations=0 flag when you call pytest. A report will be generated after your tests have run that lists how long setting up, running and tearing down each specific test took. The list is ordered from longest to shortest durations, meaning that the tests that have the most potential for being optimized will be at the top. You should focus on these tests because the longest one will determine how long it would take to run your tests even if you had an infinite amount of CPU cores.

Investigate why certain tests take a while to execute.

  • Are some tests computing something that takes a while and is computed exactly the same way by multiple tests? Precompute this result once and share it between the different tests (think of it as a fixture).
  • Are calls to a slow external API done? If you are not testing that the remote API is changing, store example responses and emulate receiving them.
  • Is there a loop in the test that runs hundreds of thousands iterations while the same test could be executed with only a thousand iterations?