Python math.isclose() to check for “almost equal”

Had an issue with checking whether a sum of floats sums up to a number, remembering that python floats are ‘special’:

>>> 0.1 + 0.2
0.30000000000000004

Stack overflow¹ told me about math.isclose(), works as you’d expect:

assert math.isclose(sum(floats), needed_sum)

unittest skip test based on condition

From unittest documentation ¹

class MyTestCase(unittest.TestCase):

    @unittest.skipIf(mylib.__version__ < (1, 3), "not supported in this library version")
    def test_format(self):
        # Tests that work for only a certain version of the library.
        pass

Google Meet

You can minimize your own video, and then make the entire window much smaller!

Python strings formatting

Obvious, but: you can declare strings and format them in separate places!

constants.py:

my_string = "Hello my name is {0}"

other_file.py:

from constants import my_string
print(my_string.format("Serhii"))

Pycharm run current unittest binding

<C-S-F10> runs the unittest where the cursor is currently located. Or all of them if located anywhere else in the file.

TODO: set binding to do the same, but debugging.

python - run only some tests from a test suite

I wanted to run only some test files, all except the ones where I needed a GPU. Wrote this:

import subprocess

# Parts of filenames to exclude
large_tests = ['component', 'test_temp']

test_folder = Path(__file__).parent.absolute()
test_files = list(test_folder.glob("test_*.py"))
test_files = [x.name for x in test_files]

for l in large_tests:
  test_files = list(filter(lambda x: l not in x, test_files))

commands = ["python3", "-m", "unittest"] + test_files

subprocess.run(commands, cwd=test_folder)

Notes:

• Thought this would be a security nightmare, but it’s not¹ - unless shell=True is explicitly passed, no shell is called, ergo no shell-command-injection stuff is possible.
• os.chdir() is nicely replaced by the cwd= parameter, much nicer than what I’d have done previously!

Python typing annotating second-order functions

def my_function(other_function: Callable) -> Callable:
  return other_function

Pycharm run all unit tests in a folder

What I’d do as

cd tests
python3 -m unittest

in Pycharm is right-clicking on a directory in Project view and “Run unittests”

OOP principles

Open/Closed principle: you should be able to open a module/class to add stuff easily, but otherwise you shouldn’t need to touch it for existing stuff.

Python dir

Wrote a line like if dir is not None .., but dir is a builtin! It returns all the names in the current scope.

Pycharm debugging

You can add Watches, values that will be shown and tracked! Nice for debugging stuff that needs values that are deep in other variables

Python unittests run at the end of the class/module

• class-level:

  • setUpClass(cls) gets called before tests from one class get run, not once per test
  • tearDownClass(cls) gets called before tests from one class get run, not once per test
  • Both need to be class methods, a la:¹

      class Test(unittest.TestCase):
          @classmethod
          def setUpClass(cls):
              cls._connection = createExpensiveConnectionObject()
    

• module-level

  • setUpModule(), tearDownModule()
  • should be implemented as normal functions

  Aaanad if you set any class variables, you can still access them as self.xxx from within the tests!

Python or in arguments

Neat thing seen in detectron default_argument_parser:

def argparser(epilog=None):
  ...
  x = epilog or "here's some text"

Where “here’s some text” is a long string that doesn’t really belong in the function signature.

A really nice pattern, much better than my usual

if x is None:
  x = ...

vim open list of files from cli

vim -p `ag -l whatever`

opens each file returned by ag. (ag -l lists only the files with matches and nothing else)

Replacing jekyll-style highlight tags with standard markdown ones

In some posts I had code blocks like {% highlight html %} etc. The html/js got parsed, and some “here’s how to redirect using javascript” code got executed in the master page.

Here’s how I replaced all that syntax with the standard markdown one:

for f in `ag -l "endhighlight"`;
do cat $f | sed "s/{% highlight \(.*\) %}/\`\`\`\1/" | sed "s/{% endhighlight %}/\`\`\`/g" > $f;
done

Python dataclasses and classmethods

@dataclass
class MyClass:
  x: int = 4

@classmethod
def init_whatever(number: int)
  return cls(x=number)

Python exceptions and unittests

unittest’s self.assertRaisesRegex() is nice but couldn’t get it to work with my custom exception class.

with self.assertRaisesRegex(CustomException, "No trained model"):

It expects the message to be in e.args¹. args also gets used by the Exception class for __str__() etc, so it’s a nice thing.

Set it up easily:

class CustomException(Exception):
    def __init__(self, detailed_message: str = None):
        if detailed_message:
          self.detailed_message = detailed_message
          self.args = (self.detailed_message, )

Catching python regex exceptions

try:
  re.search("DataLoader worker(.*is killed by signal: Bus error", text)
except re.error:
  whatever()

TODO I really like this regex tutorial: Regular Expressions: Regexes in Python (Part 2) – Real Python