Decorator [run]

Some decorator examples with type annotation.

from typing import Callable

def log(f: Callable[[int], None]) -> Callable[[int], None]:
    def inner(x: int):
        print(f"log::inner f={f.__name__} x={x}")
    return inner

def some_fn(x: int):
    print(f"some_fn x={x}")

def log_tag(tag: str) -> Callable[[Callable[[int], None]], Callable[[int], None]]:
    def decorator(f: Callable[[int], None]) -> Callable[[int], None]:
        def inner(x: int):
            print(f"log_tag::inner f={f.__name__} tag={tag} x={x}")
        return inner
    return decorator

def some_fn2(x: int):
    print(f"some_fn2 x={x}")

Walrus operator [run]

Walrus operator := added since python 3.8.

from typing import Optional

# Example 1: if let statements

def foo(ret: Optional[int]) -> Optional[int]:
    return ret

if r := foo(None):
    print(f"foo(None) -> {r}")

if r := foo(1337):
    print(f"foo(1337) -> {r}")

# Example 2: while let statements

toks = iter(['a', 'b', 'c'])
while tok := next(toks, None):

# Example 3: list comprehension

print([tok for t in ["  a", "  ", " b "] if (tok := t.strip())])

Unittest [run]

Run unittests directly from the command line as
python3 -m unittest -v test

Optionally pass -k <patter> to only run subset of tests.

# file:

import unittest

class MyTest(unittest.TestCase):
    def setUp(self):
    def tearDown(self):
    # Tests need to start with the prefix 'test'.
    def test_foo(self):
        self.assertEqual(1 + 2, 3)
    def test_bar(self):
        with self.assertRaises(IndexError):

Doctest [run]

Run doctests directly from the command line as
python -m doctest -v

# file:

def sum(a: int, b: int) -> int:
    """Sum a and b.

    >>> sum(1, 2)

    >>> sum(10, 20)
    return a + b


Micro benchmarking.

python -m timeit '[x.strip() for x in ["a ", " b"]]'