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c/python · by Vulwsztyn@programming.dev · 1y

Avoiding boilerplate by using immutable default arguments

https://vulwsztyn.codeberg.page/posts/avoiding-boilerplate-by-using-immutable-default-arguments-in-python/

Hi, I recently realised one can use immutable default arguments to avoid a chain of:

def append_to(element, to=None):
    if to is None:
        to = []

at the beginning of each function with default argument for set, list, or dict.

19 points · 7 comments · view on lemmy.world

7 Comments

Narann@jlai.lu · 4 pts · 1y (6 replies)

This is the way you're supposed to write it in Python.

It is something you get used to, yet I think it's sad.

m_f@discuss.online · 5 pts · 1y (5 replies)

You can use mutable default arguments now with a new syntax:

https://peps.python.org/pep-0671/

def bisect_right(a, x, lo=0, hi=>len(a), *, key=None):
def connect(timeout=>default_timeout):
def add_item(item, target=>[]):
def format_time(fmt, time_t=>time.time()):
Doccool@lemmy.world · 4 pts · 1y

Oh wow! This would be great I really hope it's accepted and implemented, makes a lot of sense!

Vulwsztyn@programming.dev · 3 pts · 1y

This is only a Draft for now though

Narann@jlai.lu · 3 pts · 1y (1 reply)

Does not seems to work on 3.12:

Python 3.12.11 (main, Jun 29 2025, 16:18:35) [MSC v.1944 64 bit (AMD64)] on win32
>>> def toto(tata=>[]):
  File "<stdin>", line 1
    def toto(tata=>[]):
                  ^
SyntaxError: invalid syntax
logging_strict@programming.dev · 2 pts · 1y

Upvote for the sanity check.

As the OP mentioned, this is a proposed/draft feature that may or may not ever happen.

With these kinda posts, should start a betting pool. To put money down on whether this feature sees the light of day within an agreed upon fixed time frame.

Vulwsztyn@programming.dev · 2 pts · 1y

Thank you