It's like a off-by-one error on your wedding day.
Python (REPL)
>>> >>> ... ... ... ... >>>
from plusonedecorator import plus_one
@plus_one
def cost(quantity: int, marginal_cost: float) -> float:
"""Compute the cost of production."""
return quantity * marginal_cost
cost(1000, 0.25)
251.0
>>> ... ... ... ... >>>
@plus_one
def invite(name: str, pronoun: str) -> str:
"""Decide to invite someone to your wedding."""
return f"Let's be sure to invite {name} and {pronoun}."
invite("Emilia", "her")
"Let's be sure to invite Emilia and her plus one."
>>>
invite("Maxwell", "his")
"Let's be sure to invite Maxwell and his plus one."
>>>
invite("Taylor", "their")
"Let's be sure to invite Taylor and their plus one."
(Source)