how does reduce function work in python code example

Example 1: python reduce()

#max num in list
from functools import reduce
items = [1, 24, 17, 14, 9, 32, 2]
all_max = reduce(lambda a,b: a if (a > b) else b, items)
 
print (all_max) # 32

Example 2: python reduce()

from functools import reduce
items = [1,2,3,4,5]
sum_all = reduce(lambda x,y: x + y, items)
 
print (sum_all) #15