this post was submitted on 22 Jul 2025
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Python

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Avoiding boilerplate by using immutable default arguments (vulwsztyn.codeberg.page)
submitted 1 week ago by Vulwsztyn@programming.dev to c/python@programming.dev
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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.

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[–] Narann@jlai.lu 4 points 1 week ago (7 children)

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 points 1 week ago (5 children)

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()):
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