The uses of ‘def function(*args)’ to accept an arbitrary number of positional arguments in Python

2 min readFeb 19, 2022

The aim of this page📝is to describe function definitions accepting an arbitrary number of positional arguments (not keyword here!)

1. *ARGS SYNTAX ENABLES THE ACCEPTANCE OF AN ARBITRARY NUMBER OF POSITIONAL ARGUMENTS

python function signatures can contain a special syntax called star args written as *args
i.e., the args argument is prefixed by a single asterisk
args is a widely accepted conventional name of the parameter, any other will work as well
since args is widely used for this case by convention, don't use it anywhere else
* is not used within the function body
args is called as a tuple you have to iterate over it
*args enters the function body as a tuple

if the above is called without an argument, the user will get a StopIteration exception such as

File "c:\multiplier.py", line 3, in multiplier
    result = next(i)
StopIteration

this is confusing and it exposes an implementation detail about which clients of our function should be unaware

a typical exception class for an insufficient count of arguments is TypeError
use exception chaining to transform the exception type from StopIteration to TypeError

as a sidestep, in bash you have parameter expansion that allows you to return an argument count
it is part of the standard practice to have validation at the top of the function

if [[ ! $1 ]]; then
    echo "Missing Argument"
    exit 1
fi

another approach maybe adding a regular positional argument
the absence of an argument will produce an expected TypeError
another advantage is the simplicity, no need to use an iterator
RULE: based on the above advantages, do use regular positional arguments for the required parameters (even if there is >1) and *args to deal with any extra arguments