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?
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.
Specifying a default in earlier versions of Python:
max(lst or [0])
max(lst or ['empty list'])
[1,2,3] or 'something else' is [1,2,3], but [] or 'something else' is 'something else'. If the latter is a one-item list, min() will always return its only item.
Catch and handle the exception.
try:
print(min(l), max(l))
except (ValueError, TypeError):
print('empty list or invalid input')
ValueError is raised with an empty sequence. TypeError is raised when the sequence contains unorderable types.
