A safe max() function for empty lists

Question

Evaluating,

max_val = max(a) 

will cause the error,

ValueError: max() arg is an empty sequence 

Is there a better way of safeguarding against this error other than a try, except catch?

a = [] try:     max_val = max(a) except ValueError:     max_val = default  

Answer 1

In Python 3.4+, you can use default keyword argument:

>>> max([], default=99) 99 

In lower version, you can use or:

>>> max([] or [99]) 99 

NOTE: The second approach does not work for all iterables. especially for iterator that yield nothing but considered truth value.

>>> max(iter([]) or 0) Traceback (most recent call last):   File "<stdin>", line 1, in <module> ValueError: max() arg is an empty sequence 

Answer 2

In versions of Python older than 3.4 you can use itertools.chain() to add another value to the possibly empty sequence. This will handle any empty iterable but note that it is not precisely the same as supplying the default argument as the extra value is always included:

>>> from itertools import chain >>> max(chain([42], [])) 42 

But in Python 3.4, the default is ignored if the sequence isn't empty:

>>> max([3], default=42) 3