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# python
## Decorator [[run][run-decorator]]
Some decorator examples with type annotation.
```python
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}")
f(x)
return inner
@log
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}")
f(x)
return inner
return decorator
@log_tag("some_tag")
def some_fn2(x: int):
print(f"some_fn2 x={x}")
```
## Walrus operator [[run][run-walrus]]
Walrus operator `:=` added since **python 3.8**.
```python
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):
print(f"{tok}")
# Example 3: list comprehension
print([tok for t in [" a", " ", " b "] if (tok := t.strip())])
```
## [Unittest][doc-unittest] [[run][run-unittest]]
Run unittests directly from the command line as \
`python3 -m unittest -v test`
Optionally pass `-k <patter>` to only run subset of tests.
```python
# file: test.py
import unittest
class MyTest(unittest.TestCase):
def setUp(self):
pass
def tearDown(self):
pass
# 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):
list()[0]
```
## [Doctest][doc-doctest] [[run][run-doctest]]
Run doctests directly from the command line as \
`python -m doctest -v test.py`
```python
# file: test.py
def sum(a: int, b: int) -> int:
"""Sum a and b.
>>> sum(1, 2)
3
>>> sum(10, 20)
30
"""
return a + b
```
## [timeit][doc-timeit]
Micro benchmarking.
```bash
python -m timeit '[x.strip() for x in ["a ", " b"]]'
```
[run-decorator]: https://www.online-python.com/IDdiE0gpYU
[run-walrus]: https://www.online-python.com/9T12PvmKVy
[doc-unittest]: https://docs.python.org/3/library/unittest.html
[run-unittest]: https://www.online-python.com/2fit4UcbzI
[doc-doctest]: https://docs.python.org/3/library/doctest.html
[run-doctest]: https://www.online-python.com/LZst51UNIH
[doc-timeit]: https://docs.python.org/3/library/timeit.html
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