Python Tip #288 (of 365):

Show a value's repr with "!r" in f-strings. 🧵

>>> name = "Trey"
>>> print(f"Name: {name}")
Name: Trey
>>> print(f"Name: {name!r}")
Name: 'Trey'

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Python Tip #287 (of 365):

Read tracebacks from the bottom up. 🧵

When Python encounters an exception that isn't handled in your code, it prints out a traceback.

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Python Tip #286 (of 365):

Know your way around the Python docs. 🧵

The docs at docs.python.org/3/ have many different types of pages.

It's helpful to note which kind of page you're on and consider whether you're in the right place.

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Python Tip #285 (of 365):

Learn to use the help function. 🧵

>>> help(print)
Help on built-in function print in module builtins:

print(*args, sep=' ', end='\n', file=None, flush=False)
Prints the values to a stream, or to sys.stdout by default.
...

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Python Tip #284 (of 365):

Import from another directory by adding it to sys.path. 🧵

sys.path.insert(0, str(Path(__file__).parent / "vendored_utils"))

This is a bit of a hack. It works great in your own project, but I wouldn't want to see it in an installable package.

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Python Tip #283 (of 365):

Delay slow imports until they're needed. 🧵

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Python Tip #282 (of 365):

Read your package's data files with importlib.resources. 🧵

>>> from importlib import resources
>>> resources.files("dinner").joinpath("recipes.json").read_text()
'{"tacos": ["tortillas", "beans", "salsa"]}\n'

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Python Tip #281 (of 365):

Bundle your package into one runnable file with zipapp. 🧵

$ python3 -m zipapp src -m "greet.cli:main" -p "/usr/bin/env python3" -o greet.pyz
$ python3 greet.pyz
Hello from greet!
$ ./greet.pyz
Hello from greet!

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Python Tip #280 (of 365):

Make your package runnable with a __main__‍.py file. 🧵

greet
├── cli‍.py
├── __init__‍.py
└── __main__‍.py

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Python Tip #279 (of 365):

Simplify your package's interface with __init__‍.py. 🧵

Yesterday's tip noted that an empty __init__‍.py file is common and completely fine.

But that file doesn't HAVE to be empty.

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Python Tip #278 (of 365):

Always include a __init__‍.py file in your Python packages. Even an empty one. 🧵

food_utils
├── fruits‍.py
├── __init__‍.py
└── non_fruits‍.py

A package is a directory that Python treats like a module.

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Python Tip #277 (of 365):

For substring checks, use the "in" operator. 🧵

Python has a special operator that's meant JUST for checking whether one thing is contained inside another:

>>> part = "Python"
>>> whole = "I enjoy writing Python code."
>>> part in whole
True

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Python Tip #276 (of 365):

Make self positional-only when accepting "**kwargs". 🧵

This class accepts any keyword argument... except self:

class Namespace:
def __init__(self, **kwargs):
for name, value in kwargs.items():
setattr(self, name, value)

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Python Tip #275 (of 365):

Pre-fill arguments with functools.partial. 🧵

>>> from functools import partial
>>> hex_to_int = partial(int, base=16)
>>> hex_to_int("CAFE")
51966

This is sometimes called "partially evaluating" a function.

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Python Tip #274 (of 365):

Prefer to name your functions. 🧵

Instead of this:
sorted(items, key=lambda item: int(item.split()[0]))

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Python Tip #272 (of 365):

Do something or return something, but not both. 🧵

The list sort method returns None:

>>> numbers = [4, 2, 7, 1, 5]
>>> x = numbers.sort()
>>> print(x)
None
>>> numbers
[1, 2, 4, 5, 7]

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Python Tip #273 (of 365):

Avoid needless wrapper functions. 🧵

This lambda does nothing but call len:

sorted(words, key=lambda s: len(s))

So pass len itself:

sorted(words, key=len)

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Python Tip #271 (of 365):

Return, don't print. 🧵

If your function only seems to "work" in the REPL, it may be printing when it should be RETURNING.

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Python Tip #270 (of 365):

Move and copy files with pathlib. 🧵

In Python 3.14, Path objects gained move and copy methods, and copy works on whole directories:

>>> from pathlib import Path
>>> taxes = Path("taxes")
>>> taxes.copy("taxes-backup")
PosixPath('taxes-backup')

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Python Tip #269 (of 365):

Walk directory trees with Path.walk. 🧵

The walk method (Python 3.12+) is the pathlib version of os.walk. For each directory in the tree, you get the directory's path, a list of its subdirectory names, and a list of its file names.

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