Manage empty list/invalid input when finding max/min value of list (Python)

python list error-handling max min
Jon_Computer picture Jon_Computer · Apr 13, 2014 · Viewed 22.3k times · Source

I'm finding max value and min value of a list by using max(list) and min(list) in Python. However, I wonder how to manage empty lists.

For example if the list is an empty list [], the program raises 'ValueError: min() arg is an empty sequence' but I would like to know how to make the program just print 'empty list or invalid input' instead of just crashing. How to manage those errors?

Answer

Alex Riley picture Alex Riley · Jan 3, 2015

In Python 3.4, a default keyword argument has been added to the min and max functions. This allows a value of your choosing to be returned if the functions are used on an empty list (or another iterable object). For example: 

>>> min([], default='no elements')
'no elements'

>>> max((), default=999)
999

>>> max([1, 7, 3], default=999) # 999 is not returned unless iterable is empty
7

If the default keyword is not given, a ValueError is raised instead.

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