83. Automatically passing unpacked lists or tuples to a function (or why do you see * before lists and tuples)

Basic 1 Minute

Imagine we have a very simple function that adds three numebrs together:

In [1]:
def add_three_numbers (a, b, c):
    return a + b + c

We would normally pass separate numebrs to the function, e.g.

add_three_numbers (10, 20, 35)

65

But what if our numbers are in a list or a tuple. If we pass that as a list then we are passing only a single argument, and the function declares an error:

In [3]:
my_list = [10, 20, 35]

add_three_numbers (my_list)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-900947bff326> in <module>()
      1 my_list = [10, 20, 35]
      2 
----> 3 add_three_numbers (my_list)

TypeError: add_three_numbers() missing 2 required positional arguments: 'b' and 'c'

Python allows us to pass the list or tuple with the instruction to unpack it for input into the function. We instruct Python to unpack the list/tuple with an asterix before the list/tuple:

add_three_numbers (*my_list)

65

 

 

Published by Michael Allen

Interests are use of simulation and machine learning in healthcare, currently working for the NHS and the University of Exeter. Committed to all work being performed in Free and Open Source Software (FOSS), and as much source data being made available as possible. https://gitlab.com/michaelallen1966

Published

One thought on “83. Automatically passing unpacked lists or tuples to a function (or why do you see * before lists and tuples)”

  1. Pingback: Index – Python for healthcare analytics and modelling

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